Fixes:
* Enabled buildifier on the Bazel CI again
* Added Skydocs where missing
* Moved public files out of .../private/... (e.g. cc_toolchain_config_lib.bzl)
* Reformatted
* Removed unused loads
* Using relative labels for cc_configure related files
* Added development dependency on rules_proto
* they're not in the federation yet, so hand rolling in rules_cc's WORKSPACE file
* Added development dependency on rules_python (from federation)
* Cleaned up copybara (notable change - not using @rules_cc in labels inside rules_cc repo)
* Made cc_flags_supplier usable internally
* Moved load statements to the top of the bzl file
* Moved runfiles to the tools directory
* Unified toolchain_utils.bzl and find_cc_toolchain.bzl
RELNOTES: None.
PiperOrigin-RevId: 276479521
Change-Id: I3196896061fa2ee61a3efb130c214d288782066a
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