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
  rust-lang#54517. However, it used
  `FileName::Quote` instead of `FileName::CfgSpec` which I believe was a
  mistake.
* Quote stuff was removed in
  rust-lang#51285, but did not remove
  `FileName::Quote`.
* `FileName::CfgSpec` was removed in
  rust-lang#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.

Author: ehuss

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,

compiler/rustc_span/src/lib.rs

@@ -305,8 +305,8 @@ impl RealFileName {
 #[derive(Debug, Eq, PartialEq, Clone, Ord, PartialOrd, Hash, Decodable, Encodable)]
 pub enum FileName {
     Real(RealFileName),
-    /// Call to `quote!`.
-    QuoteExpansion(Hash64),
+    /// Strings provided as `--cfg [cfgspec]`.
+    CfgSpec(Hash64),
     /// Command line.
     Anon(Hash64),
     /// Hack in `src/librustc_ast/parse.rs`.
@@ -353,7 +353,7 @@ impl fmt::Display for FileNameDisplay<'_> {
             Real(ref name) => {
                 write!(fmt, "{}", name.to_string_lossy(self.display_pref))
             }
-            QuoteExpansion(_) => write!(fmt, "<quote expansion>"),
+            CfgSpec(_) => write!(fmt, "<cfgspec>"),
             MacroExpansion(_) => write!(fmt, "<macro expansion>"),
             Anon(_) => write!(fmt, "<anon>"),
             ProcMacroSourceCode(_) => write!(fmt, "<proc-macro source code>"),
@@ -384,7 +384,7 @@ impl FileName {
             | ProcMacroSourceCode(_)
             | CliCrateAttr(_)
             | Custom(_)
-            | QuoteExpansion(_)
+            | CfgSpec(_)
             | DocTest(_, _)
             | InlineAsm(_) => false,
         }
@@ -425,7 +425,7 @@ impl FileName {
     pub fn cfg_spec_source_code(src: &str) -> FileName {
         let mut hasher = StableHasher::new();
         src.hash(&mut hasher);
-        FileName::QuoteExpansion(hasher.finish())
+        FileName::CfgSpec(hasher.finish())
     }
 
     pub fn cli_crate_attr_source_code(src: &str) -> FileName {