build: remove MSVC from Windows Bazel build actions

[anp-oai]

Intent

Windows Bazel native build actions still had a local MSVC fallback and inherited Visual Studio and Windows SDK state from the runner. This removes those system compiler dependencies and makes the local fallback match the pinned gnullvm build used with remote execution.

Parent PR: #29149

Implementation

• Move Windows host and test execution platforms to gnullvm, including the keyless local fallback.
• Remove Visual Studio discovery and compiler/SDK environment forwarding. Build actions and tests now receive separate, fixed execution and runtime paths.
• Keep cc-rs native builds on Bazel-provided Clang, llvm-ar, MinGW headers, CRT objects, and import libraries. Bazel Windows aws-lc builds always use the crate declared prebuilt NASM objects.
• Restore stack-protector flags, delete the bzip2/xz suppression patches, and add a protected C link/run probe.
• Select explicitly compatible Windows tests and Clippy helpers without --skip_incompatible_explicit_targets.

Validation

• Built the Windows stack-protector probe with --config=ci-windows-cross.
• Built zstd, ring, and aws-lc for Windows with action and host-action PATH set to a nonexistent directory.
• Inspected their configured CargoBuildScriptRun actions to verify Bazel-owned Clang, llvm-ar, MinGW headers, CRT objects, and import libraries.
• Ran the BuildBuddy wrapper unit tests and just bazel-lock-check.