Add .component <implementation constructor="..." feature

...to directly call constructor functions of ComponentContext-based C++
implementations of (non-single-instance) UNO services.  The case where these
calls would need to be bridged across different environments (e.g., from gcc3
to gcc3:affine) is not yet implemented.

bootstrap.component and expwrap.component are adapted accordingly as a proof-of-
concept (which had previously been adapted to use the prefix="direct" feature,
which may become unnecessary again in the end, depending on how to handle
single-instance services/singletons).  More to follow.

Change-Id: I18682d75bcd29d3d427e31331b4ce8161dbb846d