Add B_TRANSLATE_MARK_CONTEXT to Catalog.h and tools/CollectingCatalog.h

Fixes #13656

Signed-off-by: Adrien Destugues <pulkomandy@pulkomandy.tk>

Fix #8841 (broken localization support for 3rd-party apps).

* made private Catalog.h header public by moving it to
os/locale/tools/CollectingCatalog.h
* reintroduce B_COLLECTING_CATKEYS define (which is expected to be set
during a collectcatkeys session) in order to decide whether or not
to automatically include the CollecingCatalog.h header from Catalog.h
* adjust jam rule for collecting catalog keys accordingly

Fix #8841 (broken localization support for 3rd-party apps).

* made private Catalog.h header public by moving it to
os/locale/tools/CollectingCatalog.h
* reintroduce B_COLLECTING_CATKEYS define (which is expected to be set
during a collectcatkeys session) in order to decide whether or not
to automatically include the CollecingCatalog.h header from Catalog.h
* adjust jam rule for collecting catalog keys accordingly