fix($parse): Handle sign of -undefined consistently

When csp is disabled, evaluating `-undefined` is `-0` and when csp is enabled
the evaluation is `0`. In most cases this is not an issue as `0 === -0`, but
there is an edge case as `1/0 === Infinity` and `1/-0 === -Infinity`

Close: angular#14451

Author: lgalfaso

src/ng/parse.js

@@ -1516,7 +1516,7 @@ ASTInterpreter.prototype = {
       if (isDefined(arg)) {
         arg = -arg;
       } else {
-        arg = 0;
+        arg = -0;
       }
       return context ? {value: arg} : arg;
     };

test/ng/parseSpec.js

@@ -1755,7 +1755,7 @@ describe('parser', function() {
         expect(scope.$eval("+'1'")).toEqual(+'1');
         expect(scope.$eval("-'1'")).toEqual(-'1');
         expect(scope.$eval("+undefined")).toEqual(0);
-        expect(scope.$eval("-undefined")).toBe(0);
+        expect(scope.$eval("-undefined")).toEqual(-0);
         expect(scope.$eval("+null")).toEqual(+null);
         expect(scope.$eval("-null")).toEqual(-null);
         expect(scope.$eval("+false")).toEqual(+false);