ADD - InvalidSymbolName to migrate symbol-name({}) error to new diagnostics infraestructure

ADD - dependencies needed to port a module to new Diagnostics infra (rustc_macros, rustc_errors, errors file, and fluent file)

compiler/rustc_symbol_mangling/src/errors.rs

@@ -0,0 +1,12 @@
+//! Errors emitted by symbol_mangling.
+
+use rustc_macros::SessionDiagnostic;
+use rustc_span::Span;
+
+#[derive(SessionDiagnostic)]
+#[error(symbol_mangling::invalid_symbol_name)]
+pub struct InvalidSymbolName<'a> {
+    #[primary_span]
+    pub span: Span,
+    pub mangled_formatted: &'a str,
+}