Bring back the Rust XDR parsing check.

[dmkozh]

Description

This check has been removed in commit 4287224758c47dc6cdc0c14930754c898b886e51, however it's still necessary for most of the Core builds that support 2 protocol version.

This change reverts the removal commit and does a bit of necessary refactoring to support the new build.

Checklist

• Reviewed the contributing document
• Rebased on top of master (no merge commits)
• Ran clang-format v8.0.0 (via make format or the Visual Studio extension)
• Compiles
• Ran all tests
• If change impacts performance, include supporting evidence per the performance document

[Copilot]

Pull request overview

Restores protocol-aware Rust XDR validation while preserving pre-p28 depth behavior.

Changes:

• Adds protocol-specific XDR parsing and depth validation.
• Applies validation to regular and fee-bump transactions.
• Restores compatibility tests and centralizes protocol-link checks.

Reviewed changes

Copilot reviewed 8 out of 8 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
src/transactions/TransactionUtils.h	Declares XDR validation helper.
src/transactions/TransactionUtils.cpp	Implements protocol-aware validation.
src/transactions/TransactionFrame.cpp	Validates regular envelopes.
src/transactions/FeeBumpTransactionFrame.cpp	Validates fee-bump envelopes.
src/transactions/test/TxEnvelopeTests.cpp	Restores compatibility tests.
src/transactions/test/InvokeHostFunctionTests.cpp	Uses shared protocol-link helper.
src/test/TestUtils.h	Declares shared test helper.
src/test/TestUtils.cpp	Implements shared test helper.