Auto merge of #29767 - mukilan:fix-slowness-in-macos-copy-dependencies, r=mrobinson

Fix slowness in macos copy_dependencies

The `copy_dependencies` logic is invoking `change_non_system_libraries_path` with absolute paths to gstreamer *plugin dylibs*.
`change_non_system_libraries_path` skips editing links in servo binary to relocatable dylibs, but the since the plugins have absolute paths, they are treated as 'non-relocable' and it will try to edit the *non-existent* link (since plugins are loaded dynamically) in servo bin . These unnecessary calls to change_link_name is the cause of the slowness identified in #29764

This PR fixes the issue by ensuring plugin dylibs are not passed to the first call to change_non_system_libraries_path that patches the links in the main servo binary.

With this fix, the time taken by copy_dependencies is reduced to ~3 seconds on my system.

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<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `___` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #29764

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- [ ] There are tests for these changes OR
- [x] These changes do not require tests because they fix slowness in build step

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