Override diagnostic about baseUrl path checks

[jakebailey]

Addresses #1381 (comment)

The diagnostic generator now lets us override diagnostics for this repo, so I dropped the mention of baseUrl.

[Copilot]

Pull Request Overview

This PR updates the TypeScript compiler's diagnostic message for path validation to remove the confusing reference to 'baseUrl'. The diagnostic now provides a cleaner error message when non-relative paths are used in path mappings without the deprecated baseUrl option.

Key changes:

• Updated diagnostic message TS5090 to remove mention of baseUrl
• Modified diagnostic generation code to support overriding diagnostics by code rather than message text
• Updated all test baselines to reflect the new error message

Reviewed Changes

Copilot reviewed 36 out of 36 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
internal/diagnostics/extraDiagnosticMessages.json	Added override for TS5090 diagnostic with simplified message
internal/diagnostics/generate.go	Refactored to override diagnostics by code instead of message text
internal/diagnostics/diagnostics_generated.go	Updated generated diagnostic variable name and message text
internal/compiler/program.go	Updated reference to use new diagnostic variable name
testdata/baselines/reference/**/*.{js,txt,diff}	Updated test baselines to reflect new error message