PR: Fix pasting code in the Editor

[impact27]

Description of Changes

The paste logic does two things:

1. When pasting multiline text, it keeps the following lines at the same indentation as the first line. Exception: The following lines maximum de-dent is the smallest indentation in the clipboard.
2. For python code, it tries to avoid creating over-indented lines (created because of auto-indentation). To achieve this, it will de-dent until reaching a valid indentation. The resulting indentation can not be smaller than either:
   • The current cursor position
   • The copied indentation

• Wrote at least one-line docstrings (for any new functions)
• Added unit test(s) covering the changes (if testable)

• Included a screenshot or animation (if affecting the UI, see Licecap)

Issue(s) Resolved

Fixes #16159

Affirmation

By submitting this Pull Request or typing my (user)name below,
I affirm the Developer Certificate of Origin
with respect to all commits and content included in this PR,
and understand I am releasing the same under Spyder's MIT (Expat) license.

I certify the above statement is true and correct:

[pep8speaks]

Hello @impact27! Thanks for updating this PR. We checked the lines you've touched for PEP 8 issues, and found:

• In the file spyder/plugins/editor/widgets/codeeditor.py:

Line 2840:1: W293 blank line contains whitespace

• In the file spyder/plugins/editor/widgets/tests/test_codeeditor_1.py:

Line 174:80: E501 line too long (89 > 79 characters)
Line 175:80: E501 line too long (93 > 79 characters)
Line 176:80: E501 line too long (105 > 79 characters)
Line 200:80: E501 line too long (93 > 79 characters)
Line 201:80: E501 line too long (93 > 79 characters)
Line 202:80: E501 line too long (105 > 79 characters)

Comment last updated at 2021-08-12 16:29:54 UTC

[ccordoba12]

@impact27, thanks a lot for your help with this! It looks good to me, so please merge with 5.x to get the fix to our tests, then this should be ready.

[impact27]

Restarting the tests

[ccordoba12]

Thanks @impact27!