fix($compile): don't trim white-space in attributes

This allows developers to use white-space in their attributes, for example as value for
input[type=radio], as a separator in ngList, or as a value in any custom directive binding.
It's also consistent with the HTML spec, which allows white-space in attributes, and consistent
with Angular2, which also allows white-space in attributes.

Fixes #5513
Fixes #14539
Closes #5597

BREAKING CHANGE:

White-space in attributes is no longer trimmed automatically. This includes leading and trailing
white-space, and attributes that are purely white-space.

To migrate, attributes that require trimming must now be trimmed manually.

A common cases where stray white-space can cause problems is when
attribute values are compared, for example in an $observer:

Before:
```
$attrs.$observe('myAttr', function(newVal) {
  if (newVal === 'false') ...
});
```

To migrate, the attribute value should be trimmed manually:
```
$attrs.$observe('myAttr', function(newVal) {
  if (newVal.trim() === 'false') ...
});
```

Note that `$parse` trims expressions automatically, so attributes with expressions (e.g. directive
bindings) are unlikely to be affected by stray white-space.

src/ng/compile.js

@@ -1893,7 +1893,7 @@ function $CompileProvider($provide, $$sanitizeUriProvider) {
 
             attr = nAttrs[j];
             name = attr.name;
-            value = trim(attr.value);
+            value = attr.value;
 
             // support ngAttr attribute binding
             ngAttrName = directiveNormalize(name);

test/ng/compileSpec.js

@@ -4725,6 +4725,14 @@ describe('$compile', function() {
         expect(componentScope.attrAlias).toEqual(componentScope.attr);
       }));
 
+      it('should copy an attribute with spaces', inject(function() {
+        compile('<div><span my-component attr=" some text ">');
+
+        expect(componentScope.attr).toEqual(' some text ');
+        expect(componentScope.attrAlias).toEqual(' some text ');
+        expect(componentScope.attrAlias).toEqual(componentScope.attr);
+      }));
+
       it('should set up the interpolation before it reaches the link function', inject(function() {
         $rootScope.name = 'misko';
         compile('<div><span my-component attr="hello {{name}}">');

test/ng/directive/ngListSpec.js

@@ -130,6 +130,12 @@ describe('ngList', function() {
       helper.changeInputValueTo('a\nb');
       expect($rootScope.list).toEqual(['a','b']);
     });
+
+    it('should support splitting on whitespace', function() {
+      helper.compileInput('<textarea type="text" ng-model="list" ng-trim="false" ng-list=" "></textarea>');
+      helper.changeInputValueTo('a b');
+      expect($rootScope.list).toEqual(['a','b']);
+    })
   });
 });