Fixes #276592

Summary

• The tsconfig document link provider (cmd+click on "extends" values) now resolves module subpaths through package.json "exports" field mappings
• Previously, resolveNodeModulesPath() performed naive directory concatenation (e.g., node_modules/@scope/example/base/tsconfig.json) without consulting exports, causing resolution to fail when packages use subpath export remapping
• Added resolveViaPackageExports() that reads the module's package.json, matches the subpath against export patterns, and resolves the mapped path
• Supports exact matches (e.g., "./config") and wildcard patterns (e.g., "./*/tsconfig.json" → "./lib/*/tsconfig.json")
• Handles conditional exports by preferring types > import > require > default
• Falls back to existing direct path resolution when no exports field exists or no pattern matches

Test plan

• Create a monorepo with two packages where package A extends tsconfig from package B using exports remapping (see repro repo)
• Verify cmd+click on the "extends" value navigates to the correct file
• Verify direct subpath resolution still works for packages without exports
• Verify conditional exports (object with types/import/default keys) resolve correctly
• Verify wildcard patterns like "./*/tsconfig.json" map correctly