feat(compiler): make interpolation symbols configurable (@Component config) (#9367)

closes #9158

modules/@angular/compiler/test/expression_parser/parser_spec.ts

@@ -467,6 +467,14 @@ export function main() {
         checkInterpolation(`{{ 'foo' +\n 'bar' +\r 'baz' }}`, `{{ "foo" + "bar" + "baz" }}`);
       });
 
+      it('should support custom interpolation', () => {
+        const parser = new Parser(new Lexer());
+        const ast = parser.parseInterpolation('{% a %}', null, {start: '{%', end: '%}'}).ast as any;
+        expect(ast.strings).toEqual(['', '']);
+        expect(ast.expressions.length).toEqual(1);
+        expect(ast.expressions[0].name).toEqual('a');
+      });
+
       describe('comments', () => {
         it('should ignore comments in interpolation expressions',
            () => { checkInterpolation('{{a //comment}}', '{{ a }}'); });