[docs][clang-format] warn on \code block indentation error

There is an indentation issue in Format.h causing the html to not render correctly
It's a `\code` block in the documentation of SpacesInLineComment

- fix intentation of `SpacesInLineComment`
- warn on indentation error
- also warn on `\code` `\endcode` mismatch
- generate precise warnings
- fix some minor and style issues:
  - avoid confusion with the built-in `type` function
  - fix wrong print on `os.sys.stderr` (instead of `sys.stderr`)
  - use `with as` pattern for files

Reviewed By: MyDeveloperDay, HazardyKnusperkeks

Differential Revision: https://reviews.llvm.org/D112572