This commit adds `valueLocationReference` to function pointers and
function references. Thereby, users can navigate directly to the
pointed-to function from within the "variables" pane.
In general, it would be useful to also a add similar location references
also to member function pointers, `std::source_location`,
`std::function`, and many more. Doing so would require extending the
formatters to provide such a source code location.
There were two RFCs about this a while ago:
https://discourse.llvm.org/t/rfc-extending-formatters-with-a-source-code-reference/68375https://discourse.llvm.org/t/rfc-sbvalue-metadata-provider/68377/26
However, both RFCs ended without a conclusion. As such, this commit now
implements the lowest-hanging fruit, i.e. function pointers. If people
find it useful, I will revive the RFC afterwards.
9f8ae7844d