[GLUTEN-11885][VL] Respect custom VELOX_HOME in build info generation

[officialasishkumar]

What changes are proposed in this pull request?

Fixes #11885.

dev/gluten-build-info.sh was always reading Velox revision metadata from the default ep/build-velox/build/velox_ep checkout, even when the build used a different Velox source tree via --velox_home.

This PR updates the build-info path resolution so the Velox revision metadata is taken from the actual configured Velox checkout:

• honor an explicit backend path passed to gluten-build-info.sh
• fall back to the exported VELOX_HOME environment variable when present
• fall back to the generated cpp/build/CMakeCache.txt VELOX_HOME entry before using the default path
• quote the resolved backend path when collecting git metadata
• export VELOX_HOME from dev/builddeps-veloxbe.sh so the one-shot Velox build flow propagates the configured path into Maven's build-info generation step
• parse --velox_repo, --velox_branch, and --velox_home as scalars so VELOX_HOME can be exported to child processes correctly

How was this patch tested?

• bash -n dev/gluten-build-info.sh
• bash -n dev/builddeps-veloxbe.sh
• created a temporary standalone git repo at /tmp/fake-velox
• verified VELOX_HOME=/tmp/fake-velox bash dev/gluten-build-info.sh ... --backend velox writes the fake repo commit into gluten-build-info.properties
• verified source ./dev/builddeps-veloxbe.sh --velox_home=/tmp/fake-velox true exports VELOX_HOME for child processes

Was this patch authored or co-authored using generative AI tooling?

No

[FelixYBW]

Thank you for the fix

[philo-he]

Looks good overall. Thanks.

[philo-he]

Do we also need such modification for some other args?

[officialasishkumar]

I checked the current script again, and I do not think we need the same change for the other args in this PR. The scalar handling here matters for --velox_repo, --velox_branch, and especially --velox_home because they are reused when building VELOX_PARAMETER and when propagating VELOX_HOME to child processes. The other flags are only consumed locally in this script today. If there is another arg that also needs to cross that boundary, I can handle it in a follow-up.

[philo-he]

@officialasishkumar, thanks for the check. Since this functionality is not well covered by CI, could you verify it in local build with a custom Velox home used? You may simply check a local resource file generated by gluten-build-info.sh.