Add cancelLastOperation() API

[tikurahul]

This adds the cancelLastOperation() API. I added one extra test on the Provider frame to prove that this works. If this approach looks good, I can add more tests before I submit the change.

[codecov-io]

Codecov Report

Merging #29 into master will increase coverage by 0.15%. The diff coverage is 89.47%.

@@            Coverage Diff             @@
##           master      #29      +/-   ##
==========================================
+ Coverage   87.99%   88.14%   +0.15%     
==========================================
  Files          33       34       +1     
  Lines        1283     1350      +67     
  Branches      161      169       +8     
==========================================
+ Hits         1129     1190      +61     
- Misses        154      160       +6

Impacted Files	Coverage Δ
ts/api/cancel_last_operation_request.ts	100% <100%> (ø)
ts/api/navigator_credentials.ts	90% <100%> (+0.29%)	:arrow_up:
ts/protocol/utils.ts	81.05% <100%> (+1.5%)	:arrow_up:
ts/protocol/errors.ts	74.5% <100%> (+1.04%)	:arrow_up:
ts/protocol/rpc_messages.ts	93.61% <100%> (+0.59%)	:arrow_up:
ts/api/api.ts	82.25% <80%> (-0.41%)	:arrow_down:
ts/spi/provider_frame.ts	85.99% <85.71%> (+0.4%)	:arrow_up:

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[tikurahul]

Thanks @TMSCH !