Trim distlib to only include scripts code (#13342)

Distlib is our largest dependency. The vast majority of that is the
Windows stub executables which we can't get rid of. However, distlib
is a general purpose low-level packaging library, of which we only
use the scripts module.

By line count, trimming the parts of distlib that aren't used for
scripts results in a 5% reduction in total (`_internal` and `_vendor`)
size, which translates to ~250 KB of uncompressed and 64 KB of
compressed (wheel) savings.

Author: ichard26

pyproject.toml

@@ -137,6 +137,8 @@ drop = [
   '^pygments/cmdline\.py$',
   # trim rich's markdown support
   "rich/markdown.py",
+  # trim parts of distlib that aren't related to scripts
+  '^distlib/(?!__init__|compat|resources|scripts|util).*\.py$',
 ]
 
 [tool.vendoring.typing-stubs]