[WIP] Feature/combine autocomplete sources

[akinsho]

Looking into merging lsp completions with neovim source completions using the completion requestor interface @bryphe mentioned on discord, still early days currently this populates the menu though there are a few issues

• currently not clear that completions are sourced from vim, ?icon
• how to render the list aka 50% split user specified/configurable amount, double the list size
• create a new mode for this option? editor.completions.mode: "both/omni"

[codecov]

Codecov Report

Merging #2557 into master will decrease coverage by 5.96%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master    #2557      +/-   ##
==========================================
- Coverage   44.93%   38.97%   -5.97%     
==========================================
  Files         352      150     -202     
  Lines       14336     5614    -8722     
  Branches     1863      755    -1108     
==========================================
- Hits         6442     2188    -4254     
+ Misses       7669     3403    -4266     
+ Partials      225       23     -202

Impacted Files	Coverage Δ
.../src/Services/WindowManager/SingleSplitProvider.ts	11.11% <0%> (-88.89%)	⬇️
.../src/Services/WindowManager/layoutFromSplitInfo.ts	17.64% <0%> (-82.36%)	⬇️
.../src/Services/WindowManager/LinearSplitProvider.ts	3.89% <0%> (-81.82%)	⬇️
browser/src/Services/Sneak/SneakStore.ts	21.73% <0%> (-78.27%)	⬇️
...src/Services/Language/LanguageEditorIntegration.ts	10.34% <0%> (-75.87%)	⬇️
...vices/Learning/Achievements/AchievementsManager.ts	5% <0%> (-75%)	⬇️
browser/src/Services/InputManager.ts	20.77% <0%> (-71.43%)	⬇️
...rowser/src/Services/WindowManager/WindowManager.ts	8.18% <0%> (-67.28%)	⬇️
...Services/WindowManager/RelationalSplitNavigator.ts	5.88% <0%> (-64.71%)	⬇️
browser/src/Services/Explorer/ExplorerSelectors.ts	23.07% <0%> (-61.54%)	⬇️
... and 284 more

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