Auto merge of rust-lang#91957 - nnethercote:rm-SymbolStr, r=oli-obk

Remove `SymbolStr`

This was originally proposed in rust-lang#74554 (comment). As well as removing the icky `SymbolStr` type, it allows the removal of a lot of `&` and `*` occurrences.

Best reviewed one commit at a time.

r? `@oli-obk`

Author: bors

compiler/rustc_ast/src/util/literal.rs

@@ -35,12 +35,12 @@ impl LitKind {
                 LitKind::Bool(symbol == kw::True)
             }
             token::Byte => {
-                return unescape_byte(&symbol.as_str())
+                return unescape_byte(symbol.as_str())
                     .map(LitKind::Byte)
                     .map_err(|_| LitError::LexerError);
             }
             token::Char => {
-                return unescape_char(&symbol.as_str())
+                return unescape_char(symbol.as_str())
                     .map(LitKind::Char)
                     .map_err(|_| LitError::LexerError);
             }

compiler/rustc_ast_lowering/src/item.rs

@@ -1278,7 +1278,7 @@ impl<'hir> LoweringContext<'_, 'hir> {
     }
 
     pub(super) fn lower_abi(&mut self, abi: StrLit) -> abi::Abi {
-        abi::lookup(&abi.symbol_unescaped.as_str()).unwrap_or_else(|| {
+        abi::lookup(abi.symbol_unescaped.as_str()).unwrap_or_else(|| {
             self.error_on_invalid_abi(abi);
             abi::Abi::Rust
         })