Reduce authentication prompts for EV code signing

[nsharma1396]

Squirrel version(s) Which version(s) of the project are you using? 2.0.1 (via electron-winstaller)

Description Firstly, this is such an exceptional library! Thanks for all the work on this.

Currently, squirrel.windows iterates through each signable file and invokes signtool.exe on each file one by one. See here For EV code signing certificates, this pops up authentication on each invocation of signtool which becomes a bit hard to manage. signtool provides us the option to pass multiple file names together as space-separated so a possible improvement here can be that we create a string of space separated file names during this iteration phase and then pass it to the signtool invocation together thus reducing multiple calls to signtool as well as multiple authentication prompts for EV code signing. Can this be feasible to do here?

[parmdhoot]

This would really speed up the builds for sure!