Standardize what the `'a` thingies are called in compiler errors

[carols10cents]

There are some error messages that refer to 'a (colloquially called "lifetimes" but the compiler should be more specific) as a "lifetime annotation", a "lifetime parameter", or a "lifetime specifier".

Are these interchangeable, or is there a nuance I'm not appreciating?

If they are interchangeable, the compiler errors should probably pick one and stick with it.

Quick GitHub searches of the repo show "lifetime parameter" seems most common:

• Lifetime parameter: 372 results
• Lifetime specifier: 88 results
• Lifetime annotation: 10 results
• Lifetime name: 112 results

TRPL is inconsistent too 😅 it uses "lifetime parameter" and "lifetime annotation", but not "lifetime specifier", I don't think.

[carols10cents]

@rustbot label +A-diagnostics

[workingjubilee]

Haven't looked too closely at all the uhhh 470 cases but there might be a signifier vs. signified distinction going on there with lifetime parameter vs. lifetime specifier/annotation?

[carols10cents]

Oh there's also "lifetime name", 112 results, I'm adding that to the list in the issue description too