fix(@angular/build): resolve library bundle sourcemap sources relative to output directory

[alan-agius4]

PR Checklist

Please check to confirm your PR fulfills the following requirements:

• The commit message follows our guidelines: https://github.com/angular/angular-cli/blob/main/CONTRIBUTING.md#-commit-message-guidelines
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• Other... Please describe:

What is the current behavior?

In the @angular/build:library builder, Rolldown is invoked with a relative dir ('fesm2022' or 'types'), causing the sources paths in emitted .mjs.map and .d.ts.map files to be computed relative to <cwd>/fesm2022 and <cwd>/types rather than the actual output directory (<outputPath>/fesm2022 and <outputPath>/types).

What is the new behavior?

sourcemapPathTransform is configured to compute sourcemap sources paths relative to the actual output directory.

Does this PR introduce a breaking change?

• Yes
• No

[gemini-code-assist]

Code Review

This pull request updates the library builder pipeline to correctly resolve and relativize sourcemap paths for both ESM and DTS outputs. It introduces the outputPath parameter to executeMultiBundle and utilizes sourcemapPathTransform to transform source paths to relative POSIX paths. Additionally, the DTS bundler configuration is updated to use the 'oxc' generator, and corresponding tests are added to verify the correctness of the generated sourcemap paths. I have no feedback to provide.