Enable eslint rules: @typescript-eslint/await-thenable and @typescript-eslint/no-misused-promises

[hughns]

These rules help encourage correct handling of promises and make promise abuse more explicit.

Part of https://github.com/matrix-org/matrix-js-sdk/issues/2118

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This change is marked as an internal change (Task), so will not be included in the changelog.

[codecov-commenter]

Codecov Report

Merging #2290 (93ed2f6) into develop (5937e6a) will increase coverage by 0.00%. The diff coverage is 57.57%.

@@           Coverage Diff            @@
##           develop    #2290   +/-   ##
========================================
  Coverage    59.56%   59.57%           
========================================
  Files           91       91           
  Lines        16416    16424    +8     
  Branches      3784     3784           
========================================
+ Hits          9778     9784    +6     
- Misses        6638     6640    +2     

Impacted Files	Coverage Δ
src/http-api.ts	54.42% <0.00%> (ø)
src/crypto/dehydration.ts	11.81% <12.50%> (ø)
src/webrtc/callEventHandler.ts	8.45% <33.33%> (+0.64%)	:arrow_up:
src/models/relations.ts	50.65% <66.66%> (-0.01%)	:arrow_down:
src/webrtc/call.ts	36.14% <75.00%> (+0.03%)	:arrow_up:
src/crypto/CrossSigning.ts	83.89% <100.00%> (ø)
src/crypto/backup.ts	63.38% <100.00%> (ø)
src/crypto/index.ts	64.38% <100.00%> (+0.05%)	:arrow_up:
src/models/thread.ts	69.35% <100.00%> (+0.24%)	:arrow_up:
src/utils.ts	88.23% <100.00%> (ø)

[turt2live]

In my absence last week I missed the web meetings, was applying this rule discussed with the team?

Not to my knowledge. Code style discussion lives at https://github.com/vector-im/element-meta/pull/216 where this rule (and the inverse of this rule) aren't mentioned.

[hughns]

This was a speculative PR on my part, so do please dismiss if you wish.

It is a step towards https://github.com/matrix-org/matrix-js-sdk/pull/2291 which I believe has higher value as it identifies some possible bug sites.

[hughns]

Cleaning up this stale PR. I would still advocate for the application of the @typescript-eslint/await-thenable and @typescript-eslint/no-misused-promises rules on this project.

[t3chguy]

@hughns I suggest bringing it up in a Web Weekly meeting where it can be voted upon