Trim whitespace in RemoveLet primary span

Separate `RemoveLet` span into primary span for `let` and removal
suggestion span for `let `, so that primary span does not include
whitespace.

Fixes: #133031

Signed-off-by: Tyrone Wu <wudevelops@gmail.com>

compiler/rustc_parse/src/parser/pat.rs

@@ -685,7 +685,7 @@ impl<'a> Parser<'a> {
             self.bump();
             // Trim extra space after the `let`
             let span = lo.with_hi(self.token.span.lo());
-            self.dcx().emit_err(RemoveLet { span });
+            self.dcx().emit_err(RemoveLet { span: lo, suggestion: span });
             lo = self.token.span;
         }