[editors-kit] app-editors/geany-plugins-1.38[markdown] doesn't emerge

Nobody has claimed this yet.

```
checking for mkdio.h... yes
checking for gtk+-3.0 >= 2.16
webkit2gtk-4.0 >= 1.1.13
gthread-2.0... no
configure: error: Package requirements (gtk+-3.0 >= 2.16
webkit2gtk-4.0 >= 1.1.13
gthread-2.0) were not met:

Package 'webkit2gtk-4.0' not found

Consider adjusting the PKG_CONFIG_PATH environment variable if you
installed software in a non-standard prefix.

Alternatively, you may set the environment variables MARKDOWN_CFLAGS
and MARKDOWN_LIBS to avoid the need to call pkg-config.
See the pkg-config man page for more details.

!!! Please attach the following file when seeking support:
!!! /var/tmp/portage/app-editors/geany-plugins-1.38/work/geany-plugins-1.38/config.log
* ERROR: app-editors/geany-plugins-1.38::editors-kit failed (configure phase):
* econf failed
*
* Call stack:
* ebuild.sh, line 93: Called src_configure
* environment, line 462: Called econf '--disable-cppcheck' '--disable-extra-c-warnings' '--enable-nls' '--enable-utilslib' '--enable-addons' '--enable-autoclose' '--enable-automark' '--enable-codenav' '--enable-commander' '--enable-defineformat' '--enable-geanyextrasel' '--enable-geanyinsertnum' '--enable-geanymacro' '--enable-geanyminiscript' '--enable-geanynumberedbookmarks' '--enable-geanyprj' '--enable-geanyvc' '--enable-gtkspell' '--enable-keyrecord' '--enable-latex' '--enable-lineoperations' '--enable-lipsum' '--enable-overview' '--enable-pairtaghighlighter' '--enable-pohelper' '--enable-projectorganizer' '--enable-sendmail' '--enable-shiftcolumn' '--enable-tableconvert' '--enable-treebrowser' '--enable-vimode' '--enable-xmlsnippets' '--disable-debugger' '--enable-geanyctags' '--disable-geanydoc' '--enable-geanylua' '--enable-geanypg' '--enable-geniuspaste' '--enable-gitchangebar' '--enable-markdown' '--disable-peg-markdown' '--enable-pretty-printer' '--enable-scope' '--disable-spellcheck' '--enable-updatechecker' '--enable-workbench' '--disable-geanygendoc' '--disable-devhelp' '--disable-webhelper' '--disable-geanypy' '--disable-multiterm'
* phase-helpers.sh, line 680: Called __helpers_die 'econf failed'
* isolated-functions.sh, line 112: Called die
* The specific snippet of code:
* die "$@"
*
* If you need support, post the output of `emerge --info '=app-editors/geany-plugins-1.38::editors-kit'`,
* the complete build log and the output of `emerge -pqv '=app-editors/geany-plugins-1.38::editors-kit'`.
* The complete build log is located at '/var/tmp/portage/app-editors/geany-plugins-1.38/temp/build.log'.
* The ebuild environment file is located at '/var/tmp/portage/app-editors/geany-plugins-1.38/temp/environment'.
* Working directory: '/var/tmp/portage/app-editors/geany-plugins-1.38/work/geany-plugins-1.38'
```
We need to autogen `geany` and `geany-plugins` in order to use new webkit-gtk package.

Possible workaround for now is disable `markdown` USE.

Start by reviewing the geany and geany-plugins package definitions and how they configure the markdown plugin against the newer webkit-gtk package. Confirm the dependency and generated configuration support the webkit2gtk-4.0 requirement, then verify that the geany-plugins-1.38 markdown USE variant emerges without disabling markdown.

Written by the indexing model from the issue text.