Update jfmt and honor source tool overrides

[DanielThomas]

Summary

• update the bundled formatter to jfmt 0.8.2 and apply it to the source tree
• make source/provider tool implementations override bundled implementations in the shared runtime
• use the selected implementation for both direct and modular provider execution
• add a regression test covering a source tool with the same provider name as a bundled tool

Validation

• ja test --all (385 tests)
• targeted source-tool override, module-parent precedence, and relocatable CommandLine tests
• published jfmt 0.8.2 --check over all source modules