Backport of Ensure that SourceBundleParser always receives a relative path for the Source Directory into v1.14

[github-actions]

Backport

This PR is auto-generated from #38071 to be assessed for backporting due to the inclusion of the label 1.14-backport.

🚨

Warning automatic cherry-pick of commits failed. If the first commit failed,
you will see a blank no-op commit below. If at least one commit succeeded, you
will see the cherry-picked commits up to, not including, the commit where
the merge conflict occurred.

The person who merged in the original PR is:
@aaabdelgany
This person should resolve the merge-conflict(s) by either:

• Manually completing the cherry picks into this branch
• Creating a new branch and manually cherry-picking all commits being backported

merge conflict error: unable to process merge commit: "587fc8e66b431a9b69a57a6500b1ea1dbb83dcaf", automatic backport requires rebase workflow

The below text is copied from the body of the original PR.

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The source bundle parsing process relies on the output of sourcebundle#Bundle.LocalPathForSource to determine the source directory for a source bundle. This function can confusingly return both absolute and relative paths. It was previously assumed that this output would always be absolute -which led us to run into errors when trying to relativize an already relative path.

This PR corrects that by converting absolute paths to relative ones or leaving in the source directory as is if it's already relative.

Fixes #
#38025

Target Release

1.15.x

Rollback Plan

• If a change needs to be reverted, we will roll out an update to the code within 7 days.

Changes to Security Controls

Are there any changes to security controls (access controls, encryption, logging) in this pull request? If so, explain.

N/A

CHANGELOG entry

• This change is user-facing and I added a changelog entry.
• This change is not user-facing.

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Overview of commits

• 8a63ac9

• 1ed50c2

• 4fe0dd4

• 0f25b99

• 9a9938d

• 587fc8e

[github-actions]

Changelog Warning

Currently this PR would target a v1.15 release. Please add a changelog entry for in the .changes/v1.15 folder, or discuss which release you'd like to target with your reviewer. If you believe this change does not need a changelog entry, please add the 'no-changelog-needed' label.

[dbanck]

Thanks!

[github-actions]

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