installing generated sources (again)

[hanetzer]

Working on porting gnome's adwaita-icon-theme from an autotools build to meson.
Most of it is fairly simple, just some install_subdir calls, but a portion of the icon theme
is generated from svg files.

For this snipped of the source tree:

Adwaita/scalable
 ── actions
    ├── action-unavailable-symbolic.svg
    └── address-book-new-symbolic.svg

One would use install_subdir to place the actions directory into
/usr/share/icons/Adwaita/scalable/actions, but I'm not sure how to get this next bit to
work. A small bash snippet showing what would be done is as follows:

for size in 16x16 24x24 32x32 48x48 64x64 96x96; do
/usr/bin/gtk-encode-symbolic-svg Adwaita/scalable/actions/action-unavailable-symbolic.svg \
    $size -o $size/actions
done

Which will dump out the files action-unavailable-symbolic.symbolic.png and
address-book-new-symbolic.symbolic.png to /usr/share/icons/Adwaita/$size/actions.
The -o option merely specifies the output directory and not the filename itself, which is
autogenerated with something like ${filename%.svg}.symbolic.png in bash shell.

Once this particular port is figured out it can serve as a guide for future icon theme porting
excersizes.