Use Starlark dynamic-library symlinks in C++ linking

[dzbarsky]

Route both remaining direct _cc_internal.dynamic_library_symlink calls in cc_linking_helper.bzl through the existing Starlark dynamic_library_symlink implementation. The existing implementation preserves artifact naming, symlink registration, and its compatibility fallback for older Bazel versions.

Update the ThinLTO symlink regression to accept the Starlark Symlink action mnemonic and the native SolibSymlink compatibility fallback.

Validation: buildifier -mode=check and 89 passing ThinLTO, C++ binary, and import analysis tests.

[trybka]

@lilygorsheneva does this conflict with your changes?

[lilygorsheneva]

@lilygorsheneva does this conflict with your changes?

I missed those two callsites when making my changes. Approving.