Adds conversion functions for VCLs FontWeight, FontWidth and
FontItalic to Qt5FontFace and remove the partial "switch"
tables from KF5SalFrame.

And correctly handle the FontWidth in Qt5Font as the stretch
value, so the default font in qt5 gets the correct stretch and
doesn't look bold.

Change-Id: I698986416dff13e6dfaf9dfa7f95851b89e9137d
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/89813
Tested-by: Jenkins
Reviewed-by: Jan-Marek Glogowski <glogow@fbihome.de>

...now that macOS builds are guaranteed to have std::optional since
358146bbbd1b9775c12770fb5e497b6ec5adfc51 "Bump macOS build baseline to
Xcode 11.3 and macOS 10.14.4".

The change is done mostly mechanically with

> for i in $(git grep -Fl optional); do
>  sed -i -e 's:<o3tl/optional\.hxx>\|\"o3tl/optional\.hxx\":<optional>:' \
>   -e 's/\<o3tl::optional\>/std::optional/g' \
>   -e 's/\<o3tl::make_optional\>/std::make_optional/g' "$i"
> done
> for i in $(git grep -Flw o3tl::nullopt); do
>  sed -i -e 's/\<o3tl::nullopt\>/std::nullopt/g' "$i"
> done

(though that causes some of the resulting

  #include <optional>

to appear at different places relative to other includes than if they had been
added manually), plus a few manual modifications:

* adapt bin/find-unneeded-includes
* adapt desktop/IwyuFilter_desktop.yaml
* remove include/o3tl/optional.hxx
* quote resulting "<"/">" as "&lt;"/"&gt;" in officecfg/registry/cppheader.xsl
* and then solenv/clang-format/reformat-formatted-files

Change-Id: I68833d9f7945e57aa2bc703349cbc5a56b342273
Reviewed-on: https://gerrit.libreoffice.org/c/core/+/89165
Tested-by: Jenkins
Reviewed-by: Stephan Bergmann <sbergman@redhat.com>

...with a boost::optional fallback for Xcode < 10 (as std::optional is only
available starting with Xcode 10 according to
<https://en.cppreference.com/w/cpp/compiler_support>, and our baseline for iOS
and macOS is still Xcode 9.3 according to README.md).  And mechanically rewrite
all code to use o3tl::optional instead of boost::optional.

One immediate benefit is that disabling -Wmaybe-uninitialized for GCC as per
fed7c3deb3f4ec81f78967c2d7f3c4554398cb9d "Slience bogus
-Werror=maybe-uninitialized" should no longer be necessary (and whose check
happened to no longer trigger for GCC 10 trunk, even though that compiler would
still emit bogus -Wmaybe-uninitialized for uses of boost::optional under
--enable-optimized, which made me ponder whether this switch from
boost::optional to std::optional would be a useful thing to do; I keep that
configure.ac check for now, though, and will only remove it in a follow up
commit).

Another longer-term benefit is that the code is now already in good shape for an
eventual switch to std::optional (a switch we would have done anyway once we no
longer need to support Xcode < 10).

Only desktop/qa/desktop_lib/test_desktop_lib.cxx heavily uses
boost::property_tree::ptree::get_child_optional returning boost::optional, so
let it keep using boost::optional for now.

After a number of preceding commits have paved the way for this change, this
commit is completely mechanical, done with

> git ls-files -z | grep -vz -e '^bin/find-unneeded-includes$' -e '^configure.ac$' -e '^desktop/qa/desktop_lib/test_desktop_lib.cxx$' -e '^dictionaries$' -e '^external/' -e '^helpcontent2$' -e '^include/IwyuFilter_include.yaml$' -e '^sc/IwyuFilter_sc.yaml$' -e '^solenv/gdb/boost/optional.py$' -e '^solenv/vs/LibreOffice.natvis$' -e '^translations$' -e '\.svg$' | xargs -0 sed -i -E -e 's|\<boost(/optional)?/optional\.hpp\>|o3tl/optional.hxx|g' -e 's/\<boost(\s*)::(\s*)(make_)?optional\>/o3tl\1::\2\3optional/g' -e 's/\<boost(\s*)::(\s*)none\>/o3tl\1::\2nullopt/g'

(before committing include/o3tl/optional.hxx, and relying on some GNU features).
It excludes some files where mention of boost::optional et al should apparently
not be changed (and the sub-repo directory stubs).  It turned out that all uses
of boost::none across the code base were in combination with boost::optional, so
had all to be rewritten as o3tl::nullopt.

Change-Id: Ibfd9f4b3d5a8aee6e6eed310b988c4e5ffd8b11b
Reviewed-on: https://gerrit.libreoffice.org/84128
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>