Standardize the formatting of selector fragments to include the ':',
e.g. for - (void)foobar:(int)foobar;, report {foobar:} instead of
{foobar}{:}. This was normally the case except for a couple of places
where it was split.
This also improves integration with clangd since it relies upon the :
to identify ObjC selectors.
NOTE: It is possible to have selector fragments that are just : with
no text, we now handle this properly for the first fragment.
clang-format: please reformat the code