gdb: move "gdb:function_view" into quick-symbol.h typedefs

All users of these typedefs use them inside a gdb::function_view.  Move
the gdb::function_view in the typedefs themselves.  This shortens the
types in function signatures and helps with readability, IMO.

Rename them to remove the `_ftype` suffix: this suffix is not as
relevant in C++ as it was in C.  With function_view, the caller can pass
more than just a simple "function".  Anyway, I think it's clearer to
name them after the role the callback has (listener, matcher, etc).

Adjust some related comments.

Change-Id: Iaf9f8ede68b51ea9e4d954792e8eb90def8659a6
Approved-By: Tom Tromey <tom@tromey.com>
12 files changed