Refactor language client

[chemzqm]

Synchronize changes from vscode-langaugeclient

• Separate feature classes from client.ts, add features.ts.
• Add preInitialize() and getState to DynamicFeature and StaticFeature.
• Promise support of methods from TextDocumentSynchronizationMiddleware.
• sendProgress() and sendNotification() of language-client return Promise<void>
• Allow methods sendRequest() onRequest() sendNotification() onNotification() called before server start

[codecov[bot]]

Codecov Report

Merging #4023 (03f3f06) into master (9302171) will increase coverage by 4.51%. The diff coverage is 88.64%.

@@            Coverage Diff             @@
##           master    #4023      +/-   ##
==========================================
+ Coverage   81.26%   85.78%   +4.51%     
==========================================
  Files         232      250      +18     
  Lines       23915    23498     -417     
  Branches     5351     5335      -16     
==========================================
+ Hits        19435    20157     +722     
+ Misses       2608     1610     -998     
+ Partials     1872     1731     -141     

Impacted Files	Coverage Δ
src/handler/refactor/search.ts	93.23% <0.00%> (-0.71%)	:arrow_down:
src/language-client/client.ts	86.98% <ø> (+40.19%)	:arrow_up:
src/language-client/utils/async.ts	92.50% <ø> (ø)
src/provider/codeActionManager.ts	80.85% <0.00%> (-0.79%)	:arrow_down:
src/provider/inlayHintManager.ts	97.87% <0.00%> (-0.09%)	:arrow_down:
src/provider/signatureManager.ts	88.88% <ø> (-0.59%)	:arrow_down:
src/services.ts	23.18% <0.00%> (+0.02%)	:arrow_up:
src/snippets/parser.ts	87.15% <ø> (-0.30%)	:arrow_down:
src/snippets/string.ts	100.00% <ø> (ø)
src/sources/index.ts	79.41% <0.00%> (+10.81%)	:arrow_up:
... and 205 more

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[chemzqm]

Needs more test to see if it would break some existing coc extensions.

[chemzqm]

Should be ready to merge, @fannheyward needs your feedback.