Keep using component_getImplementationEnvironment in extensions

...instead of relying on the implicit CPPU_CURRENT_LANGUAGE_BINDING_NAME
convention.  Keeping that convention an implementation detail makes it easier to
do improvements in the future.  (Theoretically, the bundled extension in mysqlc
could be considered internal code and not adapted, but just be safe.)

Change-Id: Iae41a6e072dabc2bf7c1481ba6cfed61680edf37