...instead of by listing the content somewhat redundantly in the Rdb_*.mk
files, to avoid duplication of logic for components that are only built
conditionally (and thus should only be included conditionally in the
corresponding Rdb).  To achieve that, add an "rdb" parameter to
gb_ComponentTarget_ComponentTarget (and to the gb_*_set_componentfile macros
that internally call gb_ComponentTarget_ComponentTarget), which is used to make
the appropriate gb_Rdb_add_component call internally from within
gb_ComponentTarget_ComponentTarget.  (As a special case,
gb_CppunitTest_set_componentfile shall not call gb_Rdb_add_component, as that
has already been done by the corresponding gb_Library_set_componentfile call, so
allow the gb_ComponentTarget_ComponentTarget "rdb" parameter to be empty to
support that special case.)

Most Rdb_*.mk files are thus mostly empty now.  One exception is
i18npool/Rdb_saxparser.mk, which duplicates some of the Rdb_services content as
needed during the build in CustomTarget_i18npool/localedata.

1c9a40299d328c78c035ca63ccdf22c5c669a03b "gbuild: create services.rdb from built
components" had already tried to do something similar (in addition to other
things) under a new --enable-services-rdb-from-build option.  However, that
approach had four drawbacks that this approach here addresses (and which thus
partly reverts 1c9a40299d328c78c035ca63ccdf22c5c669a03b):

1  Rdb_services shall not contain the component files of all libraries that are
built.  While that commit filtered out the component files that go into
Rdb_ure/services (ure/Rdb_ure.mk), it failed to filter out the component files
that go into others like Rdb_postgresql-sdbc
(connectivity/Rdb_postgresql-sdbc.mk).

2  The code added by that commit to Makefile.gbuild codified the knowledge that
there is an Rdb_services, which is brittle.

3  The code added by that commit to solenv/gbuild/Rdb.mk codified the knowledge
(for gb_Rdb__URECOMPONENTS) that there is an Rdb_ure/services, which is brittle.

4  Introducing an --enable-services-rdb-from-build option needlessly provided
two different ways how the content of Rdb_services is assembled.

The changes done here would leave --enable-services-rdb-from-build as a
misnomer, as it no longer controls how Rdb_services is assembled.  I thus
renamed it to --enable-customtarget-components, as that is apparently what it
still does now.

Change-Id: Ia5e8df4b640146c77421fcec6daa11a9cd260265
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/126577
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

Just as the gtk3 plugin isn't named GNOME, rename kde5 to kf5, as
it is based on the KDE frameworks 5 libraries.

This also includes:
* a convenience alias to load the kf5 VCL plugin in case someone
  requests the kde5 plugin.
* keep convenience kde5 configure switch, but warn about it
* rename detected desktop from kde5 to plasma5

Change-Id: I6764a05b81a5edbf284484c234fee2649aacf735
Reviewed-on: https://gerrit.libreoffice.org/75313
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>