Rollup merge of #135747 - ehuss:filename-quote, r=SparrowLii

Rename FileName::QuoteExpansion to CfgSpec

I believe this variant name was used incorrectly. The timeline is roughly:

* `FileName::cfg_spec_source_code` was added in https://github.com/rust-lang/rust/pull/54517. However, it used `FileName::Quote` instead of `FileName::CfgSpec` which I believe was a mistake.
* Quote stuff was removed in https://github.com/rust-lang/rust/pull/51285, but did not remove `FileName::Quote`.
* `FileName::CfgSpec` was removed in https://github.com/rust-lang/rust/pull/116474 because it was unused.

This restores it so that the `--cfg` variant uses a name that makes more sense with how it is used, and restores what I think is the original intent.

compiler/rustc_session/src/config.rs

@@ -888,7 +888,7 @@ impl Input {
             Input::File(file) => Some(file),
             Input::Str { name, .. } => match name {
                 FileName::Real(real) => real.local_path(),
-                FileName::QuoteExpansion(_) => None,
+                FileName::CfgSpec(_) => None,
                 FileName::Anon(_) => None,
                 FileName::MacroExpansion(_) => None,
                 FileName::ProcMacroSourceCode(_) => None,