Correct click.edit typing

[AndreasBackx]

The following typing issues existed before:

• click.edit
  1. The text argument accepted bytearray but was not included in the typing.
• _termui_impl
  1. If None was inputted, str would be returned but typing suggested that it would be str if str was given and bytes if bytes was given.

This resolved an type: ignore as well.

• Add tests that demonstrate the correct behavior of the change. Tests
  should fail without the change.
• Add or update relevant docs, in the docs folder and in code.
• Add an entry in CHANGES.rst summarizing the change and linking to the issue.
  • Not going to add an entry because bytearray was always accepted, just not documented.
• Add .. versionchanged:: entries in any relevant code docs.