Add setting to run forc build on save

[sdankel]

I think this would be a useful feature. Feedback welcome!

[adlerjohn]

I was under the impression the plugin already did this. Or does it only parse?

If not then this would indeed be nice to have.

[JoshuaBatty]

We can add this feature pretty easily. Currently, we are calling forc check on every edit which compiles the program to an AST but doesn't go further in the compilation phase than that.

This feature could be a checkbox under the sway plugin settings, I feel like it should be disabled by default though and a user should opt in if they want.