refactor(compiler): don’t rely on global reflector (#16832)

Using the global reflector made it impossible
to compile multiple programs at the same time.

packages/compiler/src/compiler_util/expression_converter.ts

@@ -8,7 +8,7 @@
 
 
 import * as cdAst from '../expression_parser/ast';
-import {Identifiers, createIdentifier} from '../identifiers';
+import {Identifiers} from '../identifiers';
 import * as o from '../output/output_ast';
 
 export class EventHandlerVars { static event = o.variable('$event'); }