WIP: Add bazel info starlark-environments-proto

[hauserx]

Added bazel info starlark-environments-proto command that can be used by LSPs to obtain list of starlark symbols per starlark environment (BUILD file, .bzl file, MODULE file, etc) from running instance of bazel.

This PR needs a lot of polishing, but decided to push it early to collect comments from interested parties on related issues - CC-ing @cameron-martin, @withered-magic

Comparison between data exported by this command and data created through bazel build ...:gen_api_proto: gist

Need decision

• Decide on proto to export data in.
  Currently used builtin.Builtins for easier comparison with data created by :gen_api_proto.
  • One possibility is to use stadoc protos as suggested by @tetromino before: Add bazel help builtin-symbols-as-proto #21936 (review)
  • Far-reaching proposal is to export builtins in plain starlark that can be feed as a prelude to parsers/LSPs. This would make it more generic, but would require at least adding some syntax for specifying types (classes), and markers for native functions to starlark, and would require clients to parse this starlark code.
• Support types.
  Current implementation does not fill global.type with types, param types or return_type of callables. Need to figure out how to exactly represent types. Decision is related to deciding on the proto - for starlark protos there is a FR to add types: Stardoc protos and ModuleInfoExtractor / starlark_doc_extract should export parameter type annotations for builtin functions #21979

Dump of issues noticed that need to be fixed as well:

• Some common rule attributes are missing documentation, documentation seems to be in HTML pages for those:
  PredefinedAttributes
• Documentation for some native rules is in comments, like here:

  bazel/src/main/java/com/google/devtools/build/lib/rules/Alias.java

  Line 110 in b8073bb

  /*<!-- #BLAZE_RULE (NAME = alias, FAMILY = General)[GENERIC_RULE] -->

  and its parsed out by BuildDocCollector from source files...
• There are two forms of links, see e.g. select:
  • <a href=\"${link common-definitions#configurable-attributes}\">
  • <a href=\"../builtins/Label.html\">
• Not yet supported symbols:
  • Actions (StructsImpl), AnalysisFailureInfo, CcToolchainConfigInfo, PackageSpecificationInfo,
  • apple_common, android_common, attr, config, coverage_common, java_common
• Completely missing:
  • bind
• Missing attributes for:
  • cc_proto_library, java_binary
• Missing docs:
  • config_settings, constraint_value
• Special cases:
  • None, True, False
  • experimental_java_library_export_do_not_use
• Remove symbol names starting with _
• Remove params starting with $, also with : (:action_listener)
• Sort params - e.g. alias should have mandatory actual as one of first
• Support VENDOR file
• Support WORKSPACE file
• What with params like generator_name, are those not available and should be filtered out?
• What to do with AutoloadSymbols which does not seem to be well supported? Like android_library.