We could not rely on .ui files when generating the ninja rules for the generated UI header files. .ui files might be added to the target sources but never processed by AUTOUIC afterward, since UI header files are never included in a source code. Instead of adding dependency rules based on the .ui files, this approach scans non-generated source files for includes of the UI header files, as AUTOUIC does. This gives the consistent set of UI header files at configure time, that could be used to generate byproducts rules for the AUTOUIC. Also, the path to the generated UI header file depends not on the .ui file location but on the include line is used in source files.
Fixes: #16776
Backport: release
Topic-rename: autouic-header-depends