Refactored the way child process are executed and split the executing of 'tns' commands and triggered native builds from file watcher

[VladimirAmiorkov]

Developer notes

This PR resolves occasional issues where the NativeScript CLI cannot or wrongfully transfers the dSYM file causing debugging to not be possible for iOS.

PR features:

• Improve the 'timing' issues that could occur between child processes of the plugin and those that NativeScript CLI triggers internally by splitting them leading to the NativeScript CLI processes not being managed by the plugin during file watcher changes but only on full exit (Ctr+C)
• Above change improves the rebuild time after a change during file watching (attach & watch) by using the NativeScript CLI livesync