feat(tsc-wrapped): record original location of flattened symbols (#15367)

Added an "origins" section to the flat module `.metadata.json` files
that records where the original symbols was declared. This allows
correctly calculating relative path references recorded in metadata.

tools/@angular/tsc-wrapped/src/schema.ts

@@ -25,6 +25,7 @@ export interface ModuleMetadata {
   exports?: ModuleExportMetadata[];
   importAs?: string;
   metadata: {[name: string]: MetadataEntry};
+  origins?: {[name: string]: string};
 }
 export function isModuleMetadata(value: any): value is ModuleMetadata {
   return value && value.__symbolic === 'module';