Fix incorrectly ignored dts file from project reference for resolution

[sheetalkamat]

Port of microsoft/TypeScript#62438

[Copilot]

Pull Request Overview

This PR fixes an issue where d.ts files from project references were incorrectly ignored during module resolution. The fix ensures that both TypeScript source files and declaration files are properly included when building composite projects with project references.

• Renamed method to include both declaration and source files in the iteration
• Updated logic to process both TypeScript source files and d.ts files appropriately
• Added comprehensive test case covering project reference resolution scenarios
• Improved whitespace handling in test utility function

Reviewed Changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated no comments.

Show a summary per file

File	Description
internal/tsoptions/parsedcommandline.go	Updated method name and logic to include both d.ts and source files in project reference resolution
internal/compiler/fileloader.go	Updated method call to use the renamed function for project reference file iteration
internal/testutil/stringtestutil/stringtestutil.go	Enhanced Dedent function to handle all whitespace characters properly, not just tabs
internal/execute/tsctests/tsc_test.go	Added comprehensive test case for project reference resolution from d.ts files
testdata/baselines/reference/tsbuild/moduleResolution/resolution-from-d.ts-of-referenced-project.js	Generated test baseline showing expected behavior for the new test case