refactor(pypi): rename config settings and improve docs (bazel-contrib#2556)

Before the PR the `config_setting` names where following an internal
logic and those names would be leaking into the error messages when no
match is found. I thought that the names thus should be improved and
maybe made more similar to the `whl` filename parts that they are
derived from.

As part of this change I have also added more docs and added them to
sphinxdocs in the hopes that this documentation helps maintainers and
users looking at error messages alike.

Summary:
* Make names more similar to the whl filenames.
* Instead of having `osx_<cpu>_universal2` config settings for each
  `cpu` value, have a single `osx_universal2` config setting.
* Stop creating redundant/unused config settings
* Refactor the `_dist_config_setting` code to be simpler and create
  fewer targets by using a clever trick for the `whl` config setting
  flag value usage.

The stats:
```
$ bazel query //tests/pypi/config_settings/... | rg ":(|_)is" | wc -l
2223
$ bazel query @dev_pip//_config/... | wc -l
1982

$ bazel query //tests/pypi/config_settings/... | rg ":(|_)is" | wc -l
1780
$ bazel query @dev_pip//_config/... | wc -l
1066
```

Work towards bazel-contrib#260

Author: aignas

docs/BUILD.bazel

@@ -103,6 +103,8 @@ sphinx_stardocs(
         "//python/private:py_runtime_rule_bzl",
         "//python/private:py_test_rule_bzl",
         "//python/private/api:py_common_api_bzl",
+        "//python/private/pypi:config_settings_bzl",
+        "//python/private/pypi:pkg_aliases_bzl",
     ] + ([
         # Bazel 6 + Stardoc isn't able to parse something about the python bzlmod extension
         "//python/extensions:python_bzl",

python/private/pypi/BUILD.bazel

@@ -53,6 +53,32 @@ bzl_library(
     srcs = ["attrs.bzl"],
 )
 
+bzl_library(
+    name = "config_settings_bzl",
+    srcs = ["config_settings.bzl"],
+    deps = [
+        ":flags_bzl",
+        "//python/private:flags_bzl",
+    ],
+)
+
+bzl_library(
+    name = "deps_bzl",
+    srcs = ["deps.bzl"],
+    deps = [
+        "//python/private:bazel_tools_bzl",
+        "//python/private:glob_excludes_bzl",
+    ],
+)
+
+bzl_library(
+    name = "evaluate_markers_bzl",
+    srcs = ["evaluate_markers.bzl"],
+    deps = [
+        ":pypi_repo_utils_bzl",
+    ],
+)
+
 bzl_library(
     name = "extension_bzl",
     srcs = ["extension.bzl"],
@@ -76,29 +102,6 @@ bzl_library(
     ],
 )
 
-bzl_library(
-    name = "config_settings_bzl",
-    srcs = ["config_settings.bzl"],
-    deps = ["flags_bzl"],
-)
-
-bzl_library(
-    name = "deps_bzl",
-    srcs = ["deps.bzl"],
-    deps = [
-        "//python/private:bazel_tools_bzl",
-        "//python/private:glob_excludes_bzl",
-    ],
-)
-
-bzl_library(
-    name = "evaluate_markers_bzl",
-    srcs = ["evaluate_markers.bzl"],
-    deps = [
-        ":pypi_repo_utils_bzl",
-    ],
-)
-
 bzl_library(
     name = "flags_bzl",
     srcs = ["flags.bzl"],
@@ -245,6 +248,18 @@ bzl_library(
     srcs = ["pip_repository_attrs.bzl"],
 )
 
+bzl_library(
+    name = "pkg_aliases_bzl",
+    srcs = ["pkg_aliases.bzl"],
+    deps = [
+        ":labels_bzl",
+        ":parse_whl_name_bzl",
+        ":whl_target_platforms_bzl",
+        "//python/private:text_util_bzl",
+        "@bazel_skylib//lib:selects",
+    ],
+)
+
 bzl_library(
     name = "pypi_repo_utils_bzl",
     srcs = ["pypi_repo_utils.bzl"],