VS: Inherit target-level "-wd" flags in source files (#15284)

If a source file COMPILE_FLAGS option adds "-wd", the .vcxproj file
will have a DisableSpecificWarnings setting for the source file.
Add to the setting a reference to %(DisableSpecificWarnings) to
inherit any such flags set for the whole target.
Merge topic 'vs-inherit-wd' into next

f545eb0b VS: Inherit target-level "-wd" flags in source files (#15284)