feat($compile): add support for ng-attr with camelCased attributes

SVG attributes are case sensitive and some have upper case letters in them
This change ensures that we can identify these, when being used with the `ng-attr`
directive, by encoding upper case letters with a preceding underscore.

For example to apply `ng-attr` to the `viewBox` attribute we could write
`ng-attr-view_box` - or any of the other variants: `ng:attr:view_box`,
`data-ng-attr-view_box`, etc.

Closes #9845
Closes #10194