feat(cpp): support generator expression for SLINT_EMBED_RESOURCES & SLINT_SCALE_FACTOR

[ArcticLampyrid]

Use case:
For the higher compilation speed, we hope to use as-absolute-path in Debug but embed-files in Release.

set_property(TARGET ${PROJECT_NAME} PROPERTY SLINT_EMBED_RESOURCES $<IF:$<CONFIG:Debug>,as-absolute-path,embed-files>)

[CLAassistant]

All committers have signed the CLA.

[tronical]

Thanks!