Add Ghidra 12.0 support and fix decompiler highlighting (broken since 11.2)

[nathan-casabieille]

Problem

Since Ghidra 11.2, the plugin no longer highlights code in the decompiler view. The root cause is that `DecompilerController.callbackHandler` was made `final` in 11.2, which broke the approach of replacing it via reflection. With Java 21 (required by Ghidra 11.3+), this fails hard at runtime — `IllegalAccessException` is thrown when the plugin initialises, silently disabling decompiler highlighting entirely. Listing and function graph highlighting were unaffected.

Solution

Replace the reflection approach with `DecompilerHighlightService`, the official public API introduced in Ghidra 10.2 for exactly this use case. A `CTokenHighlightMatcher` is registered once via `createHighlighter()` and Ghidra calls it back for every token whenever a function is decompiled. The covered address set is built once per decompile pass in `start()` and looked up in O(log n) per token via `AddressSet`, which keeps things snappy even on large functions.

Changes

• `CartographerPlugin.java`: Remove all reflection-based decompiler interception. Register a `DecompilerHighlighter` through `DecompilerHighlightService` instead. `colorizeDecompiler()` now simply calls `applyHighlights()` on the highlighter, and `dispose()` cleans it up properly.
• `build.gradle`: Add support for building against both binary Ghidra releases and source tree checkouts. Add the transitive Maven dependencies that Ghidra's API signatures pull in (`guava`, `commons-lang3`, `jdom2`, etc.) as `compileOnly` so `javac` can resolve them without bundling anything extra. Fix a classpath isolation issue that caused `buildModuleHelp` to fail with a module collision error on source tree builds.
• `MIGRATION.md`: Notes on what changed and why, for anyone upgrading from an older version.
• CI: Added Ghidra 12.0 to the build matrix alongside 11.1.2.

Testing

Tested on Ghidra 12.0.4. Listing highlights, decompiler highlights, and color customisation all work as before. The `DecompilerHighlightService` API is available from Ghidra 10.2 onward, so this should not regress anything on older supported versions.