Update and create documentation in build.cmd and build.sh for CoreCLR test builds (#126951)

## Summary

Updates the help text/documentation in `src/tests/build.cmd` and
`src/tests/build.sh` for the CoreCLR test build scripts.

## Changes

### `src/tests/build.cmd`
- Added `wasm` to the list of valid build architectures in the usage
section
- Added an **OS targeting** section documenting `os <value>`, `browser`
(shorthand for `os browser`), and `wasi` (shorthand for `os wasi`)
options
- Added `-CoreCLR` to the usage section (the option was implemented in
the code but missing from the help text)

### `src/tests/build.sh`
- Added an **OS targeting** section to `usage_list` documenting the `-os
<value>` option (handled by the common build framework), listing common
OS values, and noting that native test components are automatically
skipped for mobile/device targets (`android`, `ios`, `iossimulator`,
`tvos`, `tvossimulator`)
- Added `-coreclr` to `usage_list` (the option was implemented in the
code but missing from the help text)
- Fixed escaped characters (`^(`, `^)`) and Windows-style backslashes in
path examples that were incorrectly copied from the Windows batch script

## Command sync check

| Option | build.cmd | build.sh |
|---|---|---|
| OS targeting | `os <value>`, `browser`, `wasi` | `-os <value>` (via
common framework) |
| Architecture | `x64`, `x86`, `arm64`, `wasm` | Same (via common
framework) |
| `-CoreCLR` / `-coreclr` | ✅ (now documented) | ✅ (now documented) |
| `-Mono` / `-ExcludeMonoFailures` | ✅ | ✅ |
| `-mono_aot`, `-mono_fullaot` | ❌ (Linux/macOS only) | ✅ |
| `-runtests` | ❌ (Windows: run manually via `run.cmd`) | ✅ |
| `-MSBuild` | ✅ | Use `-ninja false` via common framework |
| `-PDB` | ✅ (Windows-only PDB format) | ❌ (not applicable) |

> [!NOTE]
> This PR was generated by GitHub Copilot.

---------

Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com>
Co-authored-by: davidwrighton <10779849+davidwrighton@users.noreply.github.com>
Co-authored-by: David Wrighton <davidwr@microsoft.com>
Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: 3 people

src/tests/build.cmd

@@ -355,9 +355,15 @@ echo All arguments are optional and case-insensitive, and the '-' prefix is opti
 echo.
 echo.-? -h --help: View this message.
 echo.
-echo Build architecture: one of "x64", "x86", "arm64" ^(default: x64^).
+echo Build architecture: one of "x64", "x86", "arm64", "wasm" ^(default: x64^).
 echo Build type: one of "Debug", "Checked", "Release" ^(default: Debug^).
 echo.
+echo Build target OS options:
+echo     os ^<value^>: Set the target OS. Common values: windows ^(default^), linux, osx, android,
+echo         ios, iossimulator, tvos, tvossimulator, maccatalyst, browser, wasi.
+echo     browser: Shorthand for "os browser" ^(typically combine with "wasm", for example "wasm browser"^).
+echo     wasi: Shorthand for "os wasi" ^(typically combine with "wasm", for example "wasm wasi"^).
+echo.
 echo -Rebuild: Clean up all test artifacts prior to building tests.
 echo -SkipRestorePackages: Skip package restore.
 echo -SkipManaged: Skip the managed tests build.
@@ -374,6 +380,7 @@ echo -NativeAOT: Builds the tests for Native AOT compilation.
 echo -Perfmap: Emit perfmap symbol files when compiling the framework assemblies using Crossgen2.
 echo -AllTargets: Build managed tests for all target platforms (including test projects in which CLRTestTargetUnsupported resolves to true).
 echo -ExcludeMonoFailures, Mono: Build the tests for the Mono runtime honoring mono-specific issues.
+echo -CoreCLR: Build tests targeting the CoreCLR runtime (default; opposite of -Mono/-ExcludeMonoFailures).
 echo.
 echo     Set to "" to disable default exclusion file.
 echo -Priority ^<N^> : specify a set of tests that will be built and run, with priority N.

src/tests/build.sh

@@ -136,6 +136,12 @@ build_Tests()
 usage_list=()
 usage_list+=("All arguments are optional and the '-' prefix is optional. The options are:")
 usage_list+=("")
+usage_list+=("Build target OS: Use '-os <value>' (handled by the common build framework) to specify the")
+usage_list+=("    target OS. Common values: linux (default on Linux), osx (default on macOS), android,")
+usage_list+=("    ios, iossimulator, tvos, tvossimulator, maccatalyst, browser, wasi.")
+usage_list+=("    For mobile/device targets (android, ios, iossimulator, tvos, tvossimulator), this script")
+usage_list+=("    automatically skips building native test components.")
+usage_list+=("")
 usage_list+=("-rebuild - Clean up all test artifacts prior to building tests.")
 usage_list+=("-skiprestorepackages - Skip package restore.")
 usage_list+=("-skipmanaged - Skip the managed tests build.")
@@ -154,12 +160,13 @@ usage_list+=("-allTargets - Build managed tests for all target platforms (includ
 usage_list+=("")
 usage_list+=("-runtests - Run tests after building them.")
 usage_list+=("-mono, -excludemonofailures - Build the tests for the Mono runtime honoring mono-specific issues.")
+usage_list+=("-coreclr - Build tests targeting the CoreCLR runtime (default; opposite of -mono/-excludemonofailures).")
 usage_list+=("-mono_aot - Use Mono AOT mode.")
 usage_list+=("-mono_fullaot - Use Mono Full AOT mode.")
 usage_list+=("")
-usage_list+=("-test:xxx - Only build the specified test project ^(relative or absolute project path under src\tests^).");
-usage_list+=("-dir:xxx - Build all test projects in the given directory ^(relative or absolute directory under src\tests^).");
-usage_list+=("-tree:xxx - Build all test projects in the given subtree ^(relative or absolute directory under src\tests^).");
+usage_list+=("-test:xxx - Only build the specified test project (relative or absolute project path under src/tests).")
+usage_list+=("-dir:xxx - Build all test projects in the given directory (relative or absolute directory under src/tests).")
+usage_list+=("-tree:xxx - Build all test projects in the given subtree (relative or absolute directory under src/tests).")
 usage_list+=("-log:xxx - Base file name to use for log files (used in lab pipelines that build tests in multiple steps to retain logs for each step).")
 usage_list+=("")
 usage_list+=("Any unrecognized arguments will be passed directly to MSBuild.")