Add search in help dialog

[Saphereye]

Description

This PR adds fuzzy search to the help dialog spawned by ? shortcut.

Screenshots

Default help menu

Help menu going into search mode when / is pressed

Help menu filtered based on input query =selec

Issue

Closes: #1790

Testing

• Windows
• macOS (specify version below)
• Linux (specify distro below)
• Other (specify below)

Distro: Arch

Checklist

Ensure all of these are met:

• If this is a code change, areas your change affects have been linted using (cargo fmt)
• If this is a code change, your changes pass cargo clippy --all -- -D warnings
• If this is a code change, new tests were added if relevant
• If this is a code change, your changes pass cargo test
• The change has been tested to work (see above) and doesn't appear to break other things
• Documentation has been updated if needed (README.md, help menu, docs, configs, etc.)
• There are no merge conflicts
• You have reviewed the changes first
• The pull request passes the provided CI pipeline

Other

Currently, the search operates over all text in the help menu. That includes extra information such as the supported search types shown in the process search widget (which appears to be incorrect, for example, it claims read >= 1mb is supported, but it is not.)

I would like to know whether we can remove this extra information from the main help text or move it into a separate pane.

[codecov]

Codecov Report

❌ Patch coverage is 1.62162% with 182 lines in your changes missing coverage. Please review.
✅ Project coverage is 53.55%. Comparing base (72db123) to head (40a3e81).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
src/canvas/dialogs/help_dialog.rs	0.00%	120 Missing ⚠️
src/app.rs	0.00%	62 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1953      +/-   ##
==========================================
- Coverage   54.00%   53.55%   -0.46%     
==========================================
  Files         120      120              
  Lines       16565    16712     +147     
==========================================
+ Hits         8946     8950       +4     
- Misses       7619     7762     +143     

Flag	Coverage Δ
macos-14	46.23% <1.62%> (-0.44%)	⬇️
ubuntu-latest	51.95% <1.62%> (-0.46%)	⬇️
windows-2022	45.78% <1.62%> (-0.46%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[ClementTsang]

Sorry for the delay.

Some things I noticed when testing it:

• Spaces don't work (as in, you literally cannot type space)
• Some entries which have multiple listed keybindings will not show their entire entry
• Searching headers doesn't work (not sure if intentional)
• No cursor, ideally this should probably just copy the existing searching system for consistency

[ClementTsang]

I can take a look at these if preferred.