Update files to match new Prettier settings

[brettcannon]

The key files to review are:

1. .eslintrc
2. .prettierrc.js
3. The deletion of .prettierignore
4. package.json

[karrtikr]

LGTM

[codecov-io]

Codecov Report

Merging #15030 (c344f9c) into main (790f6d7) will increase coverage by 0%.
The diff coverage is 83%.

@@          Coverage Diff           @@
##            main   #15030   +/-   ##
======================================
  Coverage     65%      65%           
======================================
  Files        558      558           
  Lines      26226    26222    -4     
  Branches    3717     3719    +2     
======================================
- Hits       17152    17150    -2     
+ Misses      8381     8378    -3     
- Partials     693      694    +1     

Impacted Files	Coverage Δ
src/client/activation/common/analysisOptions.ts	59% <ø> (ø)
src/client/activation/common/cancellationUtils.ts	13% <ø> (ø)
...c/client/activation/common/downloadChannelRules.ts	100% <ø> (ø)
src/client/activation/jedi.ts	21% <0%> (ø)
src/client/activation/jedi/activator.ts	70% <ø> (ø)
src/client/activation/jedi/analysisOptions.ts	71% <ø> (ø)
...rc/client/activation/jedi/languageClientFactory.ts	40% <ø> (ø)
src/client/activation/jedi/languageServerProxy.ts	25% <0%> (ø)
src/client/activation/jedi/manager.ts	29% <ø> (ø)
...rc/client/activation/jedi/multiplexingActivator.ts	17% <0%> (ø)
... and 309 more