This PR uses the existing lifetime analysis for the `capture_by`
attribute.
The analysis is behind `-Wdangling-capture` warning and is disabled by
default for now. Once it is found to be stable, it will be default
enabled.
Planned followup:
- add implicit inference of this attribute on STL container methods like
`std::vector::push_back`.
- (consider) warning if capturing `X` cannot capture anything. It should
be a reference, pointer or a view type.
- refactoring temporary visitors and other related handlers.
- start discussing `__global` vs `global` in the annotation in a
separate PR.
---------
Co-authored-by: Boaz Brickner <brickner@google.com>
