Rollup merge of #118087 - GrigorenkoPV:refcell_try_map, r=Mark-Simulacrum

Add Ref/RefMut try_map method

Tracking issue:  rust-lang/rust#143801

A more generalized version of [`filter_map`](https://doc.rust-lang.org/stable/core/cell/struct.Ref.html#method.filter_map), which allows to return some data on failure.

## Safety

As far as I can tell, `E` cannot contain any `'b` data, so it is impossible to duplicate the `&'b [mut]` reference into the `RefCell`'s  data.

Other than this `E`, everything is analogous to the already stable `filter_map`.

## `Try` / `Residual`

I have considered generalizing this to use the `Try` & `Residual` just like rust-lang/rust#79711 does for `array::try_map`, but it does not seem to be possible: we want to essentially `.map_err(|e| (orig, e))` but this does not seem to be supported with `Try`. (Plus I am not even sure if it is possible to express the fact that `&U` in `Try::Output` would have to have the same lifetime as the `&T` input of `F`.)

## ACP

~As far as I can tell, this [is not mandatory](https://std-dev-guide.rust-lang.org/development/feature-lifecycle.html#suitability-for-the-standard-library), and the implementation is small enough to probably be smaller than the doc I would have to write.~

~https://github.com/rust-lang/libs-team/issues/341~

https://github.com/rust-lang/libs-team/issues/586

0 files changed, 0 insertions, 0 deletions