fix(compiler): allow tree-shakeable injectables to depend on string tokens (#22376)

Previously the injectable compiler assumed all tree-shakeable injectables
would have dependencies that were injectables or InjectionTokens. However
old code still uses string tokens (e.g. NgUpgrade and '$injector'). Using
such tokens would cause the injectable compiler to crash.

Now, the injectable compiler can properly generate a dependency on such a
string token.

PR Close #22376

packages/compiler/src/injectable_compiler.ts

@@ -55,10 +55,11 @@ export class InjectableCompiler {
           }
         }
       }
+      const tokenExpr = typeof token === 'string' ? o.literal(token) : ctx.importExpr(token);
       if (flags !== InjectFlags.Default || defaultValue !== undefined) {
-        args = [ctx.importExpr(token), o.literal(defaultValue), o.literal(flags)];
+        args = [tokenExpr, o.literal(defaultValue), o.literal(flags)];
       } else {
-        args = [ctx.importExpr(token)];
+        args = [tokenExpr];
       }
       return o.importExpr(Identifiers.inject).callFn(args);
     });