Change settings checkbox texts to positive phrasing

[ameyer0]

Type of change

• ✅ New feature (non-breaking change which adds functionality)

Description and Context

Currently, some checkbox texts in the settings use negative phrasing so it is confusing what the checkbox actually does. This pull request changes the checkboxes to have positive phrasing, and reverses their effects to match.

Current text:

• Don't mark database as modified for non-data changes
• Don't require password repeat when it's visible
• Don't hide passwords when editing them
• Don't use placeholder for empty password fields

New text:

• Mark database as modified for non-data changes
• Require password repeat when it's visible
• Hide passwords when editing them
• Use placeholder for empty password fields

Variables related to these settings have been renamed to reflect the new behavior.

This is a non-breaking change because existing installations' configurations will be upgraded while preserving the behavior the user originally set.

Fixes #3601

Screenshots

Testing strategy

• Manual testing in KDE for the GUI changes.
• Added a new unit test testUpgrade to cover updating settings from an old config file.

Checklist:

• ✅ I have read the CONTRIBUTING document. [REQUIRED]
• ✅ My code follows the code style of this project. [REQUIRED]
• ✅ All new and existing tests passed. [REQUIRED]
• ✅ I have compiled and verified my code with -DWITH_ASAN=ON. [REQUIRED]
• ✅ My change requires a change to the documentation, and I have updated it accordingly.
• ✅ I have added tests to cover my changes.

[droidmonkey]

Great work on this!

[wolframroesler]

Are you still working on this @ameyer0? If you don't have time, I could try and take care of these merge conflicts.

[ameyer0]

@wolframroesler I've been meaning to get back to it, but it'll probably be at least a week until I have time. You're welcome to try and work on the conflicts in the meantime, thanks!

[wolframroesler]

@ameyer0 Not sure what's the easiest way for me to contribute to your branch. Do I have to fork your fork of the repo and submit a PR to your branch? Maybe you have to grant me access (https://help.github.com/en/github/collaborating-with-issues-and-pull-requests/allowing-changes-to-a-pull-request-branch-created-from-a-fork)? Note that I'm not a maintainer of the keepassxc repo.

[droidmonkey]

@wolframroesler it would be easiest to checkout his branch, make your changes, then push to your own fork. Then make a new PR. We can close this one and he still gets credit for the initial commit.

[wolframroesler]

Merge conflicts solved, please have a look at #4574.