[pgAdmin4][PATCH] Refactor and change of implementation of keyboard_shortcuts function dependencies

Hi Hackers!

Attached is a patch that extracts the functions called by the
keyboard_shortcuts function extracted earlier from sqlEditor. This includes

- executeQuery
- explainAnalyze
- explain
- download
- commentBlockCode
- commentLineCode
- uncommentLineCode

There is still more work to be done, but this is it for now.

There is also an additional patch that changes the implementation of the
commentLineCode, uncommentLineCode, and commentBlockCode functions. The
shortcut

- for commentLineCode is now cmd + / (ctrl + / for Windows)
- for uncommentLineCode cmd + . (ctrl + . for Windows)
- for comment and uncomment blockCode shift + cmd + / (shift + ctrl + /
for Windows)

This is consistent with other IDEs and the way commenting is implemented.

Thanks!
Hao & Sarah