Add watching for files presented in copy rules in watch tasks

[koltyakov]

[clechner77]

I believe I ran across this today. I went in and added "copyAssetsMap" to app.json, everything copied over to DIST perfectly on build. Great! Then I realized they aren't pushed on watch....

This would be a nice addition.

[koltyakov]

Hi @clechner77,

Thanks for using the lib!

Copy assets, currently, is initiated with gulp build:copy-assets or within build all tasks. Then push tasks can be executed.

On early days in my build processes, there were a lot of assets copying to the dist, later, webpack bundling started solving most of the scenarios for me. Actually, I still use copy for fonts and images, which should not be watched as no changes applied to these files usually.

Yet, it's not complicated to implement watch on assets sources. Can do as soon as find some time for this enhancement.