Add "/" and "f" keyboard shortcuts to focus the panel filter box

[fqueze]

I would really like to be able to type 'f' in the marker chart to start filtering markers as that matches what I use a lot on treeherder, but that shortcut is already used on the panels showing samples. '/' was suggested as an alternative, but we also have plenty of existing undocumented shortcuts, so adding 'f' only in the panels where it isn't already used for something else without documenting it should be accceptable.

With the patch:

• "/" now focuses the filter input on any panel that has one (Call Tree, Flame Graph, Stack Chart, Marker Chart, Marker Table, Network Chart). The shortcut is discoverable through the input placeholder, which now reads "Enter filter terms (/)".

• "f" is an additional undocumented shortcut with the same effect, but only on panels where "f" is not already used as a call node transform shortcut (i.e. Marker Chart, Marker Table and Network Chart). It is opt-in via a new alsoFocusOnF prop on PanelSearch.

• Both shortcuts are no-ops when the user is already typing in an input, textarea or contenteditable element, and when modifier keys are held.

[codecov]

Codecov Report

❌ Patch coverage is 85.71429% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 83.48%. Comparing base (de0953b) to head (94d55df).
⚠️ Report is 22 commits behind head on main.

Files with missing lines	Patch %	Lines
src/components/shared/PanelSearch.tsx	85.71%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #6025      +/-   ##
==========================================
+ Coverage   83.47%   83.48%   +0.01%     
==========================================
  Files         342      342              
  Lines       36097    36125      +28     
  Branches    10098    10109      +11     
==========================================
+ Hits        30131    30160      +29     
+ Misses       5538     5537       -1     
  Partials      428      428              

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[flodolo]

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