Move common shim helpers to shared sources

[gerashegalov]

Related to #14834.

Description

This PR is one reviewable layer in the unshim stack introduced by #15025. It moves common shim helper implementations into shared sources now that callers have been adapted. This is the bridge between caller migration and deleting old shim-local copies.

Stack context

• Stack introduction: Add default common unshim packaging flow #15025
• Previous layer: Adapt remaining SQL plugin callers to Java helpers #15034
• Next layer: Remove old Spark 3.3.0 shim sources #15035

Testing and validation notes

• No standalone behavior change is intended in this layer. It is covered by the full-stack packaging/build validation described in Add default common unshim packaging flow #15025 and the existing tests for the affected subsystem.
• The full split stack was verified to be tree-equivalent to the pre-split stack top.

Checklists

Documentation

• Updated for new or modified user-facing features or behaviors
• No user-facing change

Testing

• Added or modified tests to cover new code paths
• Covered by existing tests
  (Covered by the validation notes in the PR description.)
• Not required

Performance

• Tests ran and results are added in the PR description
• Issue filed with a link in the PR description
• Not required