Add getWindowSize command

[mgrybyk]

Proposed changes

Added getWindowSize to choosing between getWindowSize and getWindowRect commands and be consistent with setWindowSize command.

Fixes #3905

Types of changes

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

Further comments

Affects webdriver package, requires documentation to be updated and update of webdriver, webdriverio and @wdio/sync typings to be generated.

Reviewers: @webdriverio/technical-committee

[codecov]

Codecov Report

Merging #3979 into master will increase coverage by <.01%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master    #3979      +/-   ##
==========================================
+ Coverage   98.59%   98.59%   +<.01%     
==========================================
  Files         154      155       +1     
  Lines        3492     3496       +4     
  Branches      766      767       +1     
==========================================
+ Hits         3443     3447       +4     
  Misses         44       44              
  Partials        5        5

Impacted Files	Coverage Δ
.../webdriverio/src/commands/browser/getWindowSize.js	100% <100%> (ø)

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[christian-bromann]

❤️ it 👍