Add Starlark/Buck2 related extensions

These are marked as Bazel, because there's no particular reason to treat
them as anything else.

Additionally, this expands the bazel-verse by adding a Starlark
type: https://starlark-lang.org/ which is the language used by Copybara,
Bazel, and Buck2.

This lets us annotate non-Bazel Starlark as being Starlark but not
Bazel, while Bazel Starlark is also Starlark.

.sky is used by Copybara (actually more specifically .bara.sky). .star
I've seen used in the test suite of starlark-rust, and it seems harmless
to add. lib.star is mentioned as a filename in
https://starlark-lang.org/spec.html.

Reference:
- https://buck2.build/docs/bxl/
- https://buck2.build/docs/rule_authors/package_files/

Author: lf-

identify/extensions.py

@@ -22,7 +22,8 @@
     'bmp': {'binary', 'image', 'bitmap'},
     'bz2': {'binary', 'bzip2'},
     'bz3': {'binary', 'bzip3'},
-    'bzl': {'text', 'bazel'},
+    'bxl': {'text', 'bazel'},
+    'bzl': {'text', 'bazel', 'starlark'},
     'c': {'text', 'c'},
     'c++': {'text', 'c++'},
     'c++m': {'text', 'c++'},
@@ -247,6 +248,7 @@
     'scm': {'text', 'scheme'},
     'scss': {'text', 'scss'},
     'sh': {'text', 'shell'},
+    'sky': {'text', 'starlark'},
     'sln': {'text', 'sln'},
     'slnx': {'text', 'xml', 'slnx', 'msbuild'},
     'sls': {'text', 'salt'},
@@ -255,6 +257,7 @@
     'spec': {'text', 'spec'},
     'sql': {'text', 'sql'},
     'ss': {'text', 'scheme'},
+    'star': {'text', 'starlark'},
     'sty': {'text', 'tex'},
     'styl': {'text', 'stylus'},
     'sv': {'text', 'system-verilog'},
@@ -390,6 +393,7 @@
     'bblayers.conf': EXTENSIONS['bb'],
     'bitbake.conf': EXTENSIONS['bb'],
     'Brewfile': EXTENSIONS['rb'],
+    'BUCK': EXTENSIONS['bzl'],
     'BUILD': EXTENSIONS['bzl'],
     'Cargo.toml': EXTENSIONS['toml'] | {'cargo'},
     'Cargo.lock': EXTENSIONS['toml'] | {'cargo-lock'},
@@ -398,7 +402,6 @@
     'config.ru': EXTENSIONS['rb'],
     'Containerfile': {'text', 'dockerfile'},
     'CONTRIBUTING': EXTENSIONS['txt'],
-    'copy.bara.sky': EXTENSIONS['bzl'],
     'COPYING': EXTENSIONS['txt'],
     'Dockerfile': {'text', 'dockerfile'},
     'direnvrc': EXTENSIONS['bash'],
@@ -418,6 +421,7 @@
     'makefile': EXTENSIONS['mk'],
     'NEWS': EXTENSIONS['txt'],
     'NOTICE': EXTENSIONS['txt'],
+    'PACKAGE': EXTENSIONS['bzl'],
     'PATENTS': EXTENSIONS['txt'],
     'Pipfile': EXTENSIONS['toml'],
     'Pipfile.lock': EXTENSIONS['json'],