Add regenerate-override-patches.sh to automate coupled override-patch regeneration

[xyos]

Issue

Description of Changes

Adds scripts/patches/regenerate-override-patches.sh, which automates regenerating @generated override patches and healing the rest of the quilt series.

Background: patches generated by scripts/patches/apply-override.sh rewrite shared blocks in package.json (for example the root overrides object). Changing the version in one such patch invalidates the diff context of every later @generated patch in the series, which today means a slow manual conflict-resolution loop with quilt push -f / edit / quilt refresh per patch.

The new script makes this a single command:

scripts/patches/regenerate-override-patches.sh \
  --set 'undici=^7.30.0' \
  common/finding-override-undici.diff

Behavior:

• Each named patch must be an existing @generated patch. The script re-reads the apply-override.sh command stored in the patch's @generator metadata line and re-executes it (the free-text header is extracted from the patch and re-passed via --header).
• --set 'PACKAGE=VERSION' (repeatable) rewrites the version for that package in the named patches' @generator specs and header text before regenerating, so a version bump needs no manual edits.
• After each regeneration it runs prepare-src.sh --command rebase_patches <target>. If the rebase stops on a conflicted patch that is itself @generated, the script force-pops it, empties the stale patch file, and regenerates it deterministically from its own @generator line, then rebases again (capped at 25 iterations). If the conflicted patch is not @generated, it stops and prints the manual quilt refresh instructions.
• --target <t> selects the series to rebase (default code-editor-sagemaker-server); --dry-run prints every command it would run without executing.

Also updates apply-override.sh to honor a pre-set QUILT_SERIES instead of always picking the first *.series file found, so the target's series is respected (falls back to the old behavior when unset).

Testing

All runs inside the code-editor-ubuntu container against a full checkout:

• Dry run (--dry-run --set 'undici=^7.29.0' --set 'ip-address=^10.3.1' common/finding-override-undici.diff common/finding-override-ip-address.diff): exits 0 and prints the exact apply-override.sh / prepare-src.sh commands it would execute.
• Idempotent run (re-setting the current versions with the same command minus --dry-run): exits 0, git diff on the two named patches is empty, and a strict ./scripts/prepare-src.sh code-editor-sagemaker-server passes afterwards.
• Heal-path run (--set 'undici=^7.30.0' common/finding-override-undici.diff): the bump broke the context of finding-override-form-data.diff and then finding-override-tar.diff; both were regenerated automatically from their own @generator lines, the loop converged in 4 rebase iterations, exit 0, and strict prepare-src.sh passes with ^7.30.0 present in the header, @generator, @override-package, and all hunks of the undici patch.
• Error paths: unknown --target, non-@generated patch, and missing patch arguments all fail fast with clear messages.

Screenshots/Videos

Additional Notes

The rebase loop reuses prepare-src.sh --command rebase_patches, which refreshes each patch as it re-applies. On a tree with mixed diff-header styles this can normalize the headers of a few untouched patches on the first run; the result is deterministic and stable on subsequent runs.

Backporting

Not needed; developer tooling only.

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