Bug 242903

When using gi-docgen (after bug #239016), it will use the first paragraph
of a documentation comment as the “brief” description an entity (function,
struct, etc.). Many are already fine, but gtk-doc (which we used before)
did not work in the same way, which means a number of documentation comments
are missing a brief description, or the existing one is too long and usually
should be taken as long description instead.

It would be good to find the items with missing brief descriptions and add
them. One idea to avoid reading all the documentation comments manually
would be to make a script that parses the .gir XML used as input for gi-docgen
which detects items with only one paragraph, or more than one paragraph but
the first one is too long (more than 80-90 characters, or a similar check.)