x11/tilda: Promote vte3 from BUILD_DEPENDS to include RUN_DEPENDS

User got error message, 'Shared object "libvte-2.91.so.0" not found,
required by tilda' when launching tilda. Manually installing
x11-toolkits/vte3 fixed the issue, so vte3 is clearly more than a
build dependency. I've specified RUN_DEPENDS rather than convert
BUILD_* to LIB_* given how vte3 was already specified and the fact
there's no generic library in pkg-plist.

while here, fix the pkg-plist error that showed during build testing
by adding share/appdata/tilda.appdata.xml to the list

approved by: just fix it.