[feature request] Consider moving `bzl_library.bzl` into `@bazel_tools`

### Description of the feature request:

Skylib's [`bzl_library.bzl`](https://github.com/bazelbuild/bazel-skylib/blob/1.4.1/bzl_library.bzl) provides a `StarlarkLibraryInfo` provider and `bzl_library` rule, which are used for aggregating `.bzl` rules files for use by other analysis tools.

The definition of that provider and rule are quite stable (basically unchanged since 2018), and it has no dependencies on any other part of skylib.

The natural way to use that file is to `load` it from every `BUILD` file in a ruleset, like this:

```python
# rules_example/example/BUILD
load("@bazel_skylib//:bzl_library.bzl", "bzl_library")

bzl_library(
name = "bzl_srcs",
srcs = ["defs.bzl", "repository.bzl", "toolchain.bzl"],
deps = ["//example/internal:bzl_srcs"],
)
```

However, since the `load` needs to fetch skylib before evaluation continues, this means that skylib becomes a hard dependency for _every client of the ruleset_.

Given that the `bzl_library.bzl` file is generic, broadly useful, and very stable, could it be bundled into `@bazel_tools` instead?

Start by reviewing the linked Skylib bzl_library.bzl file and how Bazel currently exposes @bazel_tools. Trace how rulesets load this file and identify the compatibility and packaging implications of bundling it with Bazel. Done means a decided, validated approach for providing the provider and rule without requiring Skylib.

Written by the indexing model from the issue text.