* New iwyu binary that outputs "missing includes" as in includes that couldnt be seen from a specific file but that iwyu believes should be included (Definition.h for example is included through response file)
* Fixed so files that has Definitions.h as missing include and has no other includes add HAL/Platform.h. This handles situations with headers only having _API as a dependency
* Added -PathToUpdateFile which can be used to provide all the paths to update through a text file.
* Added so -PathToUpdate can take in multiple semi colon separated paths
* Added special handling for files that only has one include which is some custom define turning into an include.
* Added so if processing of any file fail we early out with an error
#preflight skipped
#rb none
[CL 23674846 by henrik karlsson in ue5-main branch]