…el-contrib#3851)

This builds on the existing `py-extension` branch. It adds support for
platform and abi tags in the resulting library filename. The
`:py_extension_test`, `:py_extension_analysis_tests`, and
`:py_limited_api_tests` test targets in `//tests/cc/py_extension` now
build and pass.

Relates to bazel-contrib#3283

…tension (bazel-contrib#3875)

Per feedback from bazel-contrib#3851, this PR re-works the platform detection logic
to rely on platform constraints instead of the Python runtime/toolchain.

### Description

This PR contains updates to the experimental `py_extension`
implementation. It re-works the platform tag detection to rely on modern
platform constraints, and refactors the compilation and linking
mechanism
to delegate to Bazel's native `cc_shared_library` and `cc_library`
rules.

This PR targets the main repository's `py-extension` branch (not
`main`).

### Key Changes

#### 1. Platform Tag & ABI Tag Derivation
* **Introduced `abi_tag` to `PyCcToolchainInfo`**: Added the `abi_tag`
field to the `PyCcToolchainInfo` provider, populated by the
`py_cc_toolchain` rule. It defaults to deriving the tag from
`python_version` (e.g. `cpython-311`) for backward compatibility.
* **Constraint-Based Detection**: Replaced legacy parsing of
`cc_toolchain` CPU names with direct lookup in rules_python's central
`PLATFORMS` registry using platform constraints.
* **Limited API Configuration**: Updated how limited API (`.abi3.so`)
suffixes are appended based on the toolchain configuration.

#### 2. Compilation & Linking Delegation (Refactor to
`cc_shared_library`)
* **Macro Fusion**: Replaced the custom linking logic in the
`py_extension` rule with a macro of the same name. It now accepts C/C++
source/header files directly (`srcs`, `hdrs`, `copts`, `defines`),
implicitly wrapping them in a private `cc_library` under the hood.
* **Consolidated Attributes**: Consolidated static linkage under
standard `deps` (removing the redundant `static_deps` attribute) and
aligned linker arguments with `cc_shared_library`'s `user_link_flags`.
* **Wrapper Rule (`_py_extension_wrapper`)**: Added a lightweight,
private rule that wraps the `cc_shared_library` output to:
* Query the Python toolchain for platform/ABI tags to resolve PEP 3149
compliant filenames (e.g. `.cpython-311-x86_64-linux-gnu.so` or
`.abi3.so`).
*   Create a cheap `symlink` from the CSL output to the PEP 3149 name.
* Propagate `PyInfo` (for python rules) and `CcSharedLibraryInfo` (for
dynamic C++ dependencies).
* **ODR Validation**: Leveraging native `cc_shared_library` ensures
strict analysis-time validation against One Definition Rule (ODR)
violations (e.g., duplicate static linkage in dynamic chains).

#### 3. Runfiles and Data Support
* **Runfiles Propagation**: Re-implemented runfiles collection using the
repository's standard `builders.RunfilesBuilder` to support runtime
assets (`data` attribute) and dynamic library dependency
propagation.

### Verification & Testing
* Added parity test cases in `dependency_graph_tests.bzl` to verify
dynamic dependency chains and static sharing behavior.
* Added runfiles validation in `py_extension_tests.bzl` to verify data
asset propagation.
*   Updated limited API tests to match CSL output structure.
* All 14 tests in `//tests/cc/py_extension/...` are compiling and
passing.
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TAG=agy
CONV=23f8a5e8-2d99-401a-9903-1256b7d42b0e

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Co-authored-by: gemini-code-assist[bot] <176961590+gemini-code-assist[bot]@users.noreply.github.com>