Implement mouse keybinds

[xDarksome]

This PR:

• generalizes lapce-data/keypress module to be able to handle both keyboard and mouse presses
• makes MouseForward/MouseBackward/MouseMiddle available to binding (via config and KeyMap UI)
• wires up those bindings to the Editor widget

The bindings are currently only wired to the Editor widget as it's sufficient for my use case, and I'm not sure whether this feature is needed in other widgets.

• Added an entry to CHANGELOG.md if this change could be valuable to users

[codecov-commenter]

Codecov Report

Merging #1835 (0732024) into master (19cefff) will increase coverage by 0.55%.
The diff coverage is 26.04%.

@@            Coverage Diff            @@
##           master   #1835      +/-   ##
=========================================
+ Coverage    6.39%   6.94%   +0.55%     
=========================================
  Files         128     128              
  Lines       55408   55515     +107     
=========================================
+ Hits         3542    3858     +316     
+ Misses      51866   51657     -209     

Impacted Files	Coverage Δ
lapce-data/src/keypress/mod.rs	15.90% <0.00%> (-0.49%)	⬇️
lapce-ui/src/editor.rs	0.00% <0.00%> (ø)
lapce-ui/src/keymap.rs	0.00% <0.00%> (ø)
lapce-ui/src/tab.rs	0.00% <0.00%> (ø)
lapce-data/src/keypress/keypress.rs	73.23% <37.20%> (+60.35%)	⬆️
lapce-data/src/keypress/loader.rs	86.20% <100.00%> (+1.59%)	⬆️

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