C++ template completion support v3

[Keith Seitz]

On 2/18/22 12:34, Tom Tromey wrote:
> 
> Sorry about the delay on this.
> I think this is OK.

Haha. That makes two of us! ;-)

I will work with Eli to finalize the documentation
before pushing.

However, with gdb-12 on the horizon, would it be preferred
to wait on pushing this until after branching has occurred?

IMO, this is a pretty straightforward feature, but that's just
my $0.00002.

Keith