fix(tsoptions): validate project reference fields

[TorinAsakura]

Summary

• Validate project reference path and circular fields before constructing ProjectReference values.
• Report diagnostics for missing, non-string, or empty reference.path instead of silently dropping the reference or panicking.
• Report diagnostics for non-boolean reference.circular.
• Cover invalid project reference diagnostics in tsc and tsc --build baseline tests.

Fixes #4269.

Before

A project reference with a non-string path could panic while parsing the config:

panic: interface conversion: interface {} is bool, not string
...
internal/tsoptions.parseProjectReference

A project reference with an empty path was silently omitted from the build graph:

Projects in this build:
    * <tmp>/flat/tsconfig.build.json

After

Invalid project reference fields are reported as config diagnostics instead of panicking; the repro includes the referenced config so this only shows the project-reference field diagnostics:

<tmp>/flat/tsconfig.json(1,43): error TS5024: Compiler option 'reference.path' requires a value of type string.
<tmp>/flat/tsconfig.json(1,49): error TS5024: Compiler option 'reference.path' requires a value of type string.
<tmp>/flat/tsconfig.json(1,96): error TS5024: Compiler option 'reference.circular' requires a value of type boolean.
<tmp>/flat/tsconfig.json(1,111): error TS18051: Compiler option 'reference.path' cannot be given an empty string.
exit status 2

An empty project reference path is now diagnosed instead of silently ignored:

<tmp>/flat/tsconfig.build.json(1,24): error TS18051: Compiler option 'reference.path' cannot be given an empty string.
exit status 2

Validation

• go test ./internal/execute/tsctests -run 'TestTscProjectReferences|TestBuildConfigFileErrors'
• go test ./internal/tsoptions ./internal/execute/...

[Copilot]

Pull request overview

This PR hardens tsconfig project reference parsing in internal/tsoptions by validating references[].path and references[].circular before constructing core.ProjectReference entries, converting previously panicking/silent-failure scenarios into config diagnostics (Fixes #4269).

Changes:

• Added typed/empty-string validation for references[].path and type validation for references[].circular, emitting appropriate diagnostics instead of panicking or omitting references.
• Introduced a helper to attach diagnostics to the most relevant references[] property node when parsing from a JSON SourceFile.
• Added unit tests covering invalid project reference fields for both source-file parsing and object-based config parsing.

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated no comments.

File	Description
internal/tsoptions/tsconfigparsing.go	Validates references entries, emits targeted diagnostics, and adds a helper for precise diagnostic locations.
internal/tsoptions/tsconfigparsing_test.go	Adds test coverage for invalid references[].path / references[].circular across both config parsing entry points.
internal/tsoptions/parsinghelpers.go	Makes project reference parsing type-safe by returning a structured parse result instead of using unsafe type assertions.

[Copilot]

Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated no new comments.