Merge bitcoin/bitcoin#21740: test: add new python linter to check file names and permissions

46b025e test: add new python linter to check file names and permissions (windsok)
6f6bb3e test: fix file permissions on various scripts (windsok)

Pull request description:

  Adds a new python linter test which tests for correct filenames and file permissions in the repository.

  Replaces the existing tests in the `test/lint/lint-filenames.sh` and `test/lint/lint-shebang.sh` linter tests, as well as adding some new and increased testing. This increased coverage is intended to catch issues such as in #21728 and https://github.com/bitcoin/bitcoin/pull/16807/files#r345547050

  Summary of tests:
  * Checks every file in the repository against an allowed regexp to make sure only lowercase or uppercase alphanumerics (a-zA-Z0-9), underscores (_), hyphens (-), at (@) and dots (.) are used in repository filenames.

  * Checks only source files (*.cpp, *.h, *.py, *.sh) against a stricter allowed regexp to make sure only lowercase alphanumerics (a-z0-9), underscores (_), hyphens (-) and dots (.) are used in source code filenames. Additionally there is an exception regexp for directories or files which are excepted from matching this regexp (This should replicate the existing `test/lint/lint-filenames.sh` test)

  * Checks all files in the repository match an allowed executable or non-executable file permission octal. Additionally checks that for executable files, the file contains a shebang line.

  * Checks that for executable `.py` and `.sh` files, the shebang line used matches an allowable list of shebangs (This should replicate the existing `test/lint/lint-shebang.sh` test)

  * Checks every file that contains a shebang line to ensure it has an executable permission

  Additionally updates the permissions on various files to comply with the new tests.

  Fixes #21729

ACKs for top commit:
  practicalswift:
    cr re-ACK 46b025e: patch still looks correct
  kiminuo:
    code review ACK 46b025e if `contrib/gitian-descriptors/assign_DISTNAME` permission change is deemed OK.
  laanwj:
    Code review ACK 46b025e

Tree-SHA512: 1c8201a2cee0d9cbce15652b68cec9a6458a8b493fcd5392f98560aca0b1a12e668baab65a47100f116f626dadc3f591deb47f7368468c6a46c6c712c2533455

Author: laanwj