UI: Add Search by Hotkey filter and Hotkey Duplicate Detection

[furious]

Description

Implemented a duplicate detection that shows a warning indicator inside the Hotkey field, clicking on that icon will filter all actions with the same Hotkey.
Also added a standalone search field so users can find anything by Hotkeys.
Improved the hotkey listing, now all hotkeys are inside a scroll area so the filters stay on the top always.

Motivation and Context

Hotkey Duplicate Detection

Fixes #5081

How Has This Been Tested?

Windows 10, compiled and run

On the hotkeys settings, put the same hotkey in random actions, it shows a warning icon inside the field telling its being used by other actions.
Clicking on the icon will only show actions with the same hotkey. Same effect as you search by the hotkey filter.

Types of changes

New feature (non-breaking change which adds functionality)
Tweak (non-breaking change to improve existing functionality)

Checklist:

• My code has been run through clang-format.
• I have read the contributing document.
• My code is not on the master branch.
• The code has been tested.
• All commit messages are properly formatted and commits squashed where appropriate.
• I have included updates to all appropriate documentation.

[ghost]

I've found an issue: First filter by a hotkey, then enter a search term into the normal filter.
If you do it in that order, you will see that it will show all items again matching the normal filter, ignoring the hotkey filter.
When you then re-enter the filtered hotkey, everything works correctly.

[furious]

Fixed the issue mentioned by @Vainock, now both filters work together.
Change the warning text as @Fenrirthviti suggested on the discussion thread.

[jp9000]

I made some minor modifications before merging.

• I reduced the iteration count within ScanHotkeys. It was O(n2) before which was really not optimal.
• It now disregards duplicates from hotkey pairs, because pairs were intended to share hotkeys
• The icon is now only created once in OBSBasicSettings, then shared among all the hotkeys, which will help create hotkey widgets much faster
• Every hotkey widget was being redrawn every single time ScanHotkeys was called, which is really not optimal. Instead, I changed it so that it checks to see if the duplicate state has changed since last update, and only update the widget in that specific case.
• I made the code a little bit less indented/squishy. If you run clang-format and you see your code becoming really squished, that probably means you need to split the code you're writing off into a separate function

Keep in mind that there are some users that have a very large number of scenes/sources, thus they can have a lot of hotkeys, so the hotkeys window was already unoptimal as it was. Even with my added optimizations, it will still have an impact on users who have a large number of hotkeys. This is not really your fault or anything, just kind of a symptom of creating/showing every single hotkey all in one go.

I need to note again to everyone else that we need to switch the hotkeys section to a listview or gridview of some sort where we can add hotkeys to that box contextually rather than show every potential hotkey all at once. The current method is just not optimal for people with large number of sources/etc.