Clarify outlives rules on opaques with specified bounds

There is some subtlety in describing the mechanics of the outlives
rules for `impl Trait` opaque types.  In our description of these
rules for opaque types that include a specified outlives bound, we had
some words that were less clear than we had intended.  Let's change
those words around to make the meaning more clear.

Specifically, rather saying that "it" outlives the specified lifetime,
what we mean exactly is that the lifetime that's substituted for the
specified lifetime parameter must outlive that other lifetime.

Note that none of this language is normative.  These rules have all
been specified in earlier RFCs.

Author: traviscross

text/3498-lifetime-capture-rules-2024.md

@@ -32,7 +32,7 @@ In the above, we would say that the lifetime parameter `'a` has been captured in
 
 For an opaque type that *does not* specify an outlives bound (e.g. `+ 'other`), when a caller receives a value of that opaque type and wants to prove that it outlives some lifetime, the caller must prove that all of the captured lifetime components of the opaque type outlive that lifetime.  The captured lifetime components are the set of lifetimes contained within captured type parameters and the lifetimes represented by captured lifetime parameters.
 
-For an opaque type that *does* specify an outlives bound (e.g. `+ 'other`), when a caller receives a value of that opaque type and wants to prove that it outlives some lifetime, it's enough to prove that it outlives the specified lifetime in the bounds of the opaque after transitively taking into account all known lifetime bounds.  For such an opaque type, the *callee* must prove that all lifetime and type parameters that are used in the hidden type outlive the specified bound.
+For an opaque type that *does* specify an outlives bound (e.g. `+ 'other`), when a caller receives a value of that opaque type and wants to prove that it outlives some lifetime, it's enough to prove that the lifetime substituted for the specified lifetime parameter in the bounds of the opaque outlives that other lifetime after transitively taking into account all known lifetime bounds.  For such an opaque type, the *callee* must prove that all lifetime and type parameters that are used in the hidden type outlive the specified bound.
 
 ## Capturing lifetimes in type parameters