build: use xml-stripblanks with .ui resources

This adds a preprocess step to the .ui files to strip them of blank characters. It also removes the compressed='true' from the .ui files since that involves creating lots of decompressor objects when creating widgets. Doing so has runtime overhead and slows down the creation of initial application windows.

The .ui files are left compressed for the Inspector, since that is not in the core performance path of application startup.