ag-Grid does not work in IE 11 and config entity should be more open for admin (xss::filteradmin)

Problem/Motivation

ag-Grid is not opening on IE due to an error with "assign."
ag-Grid has some abilities that require code to be added into JSON. However, this is filtered out. Since the config entity is an admin only function, then the output from these items should be xss filtered as such.

Proposed resolution

JSON merge with Object.assign should be replaced by $.extend for IE compatibility

ag-Grid config entities will be filtered with xss::filteradmin. When testing code in columnDefs per documentation from ag-Grid, it's not considered a standard JSON data type, so PHP is unable to switch the JSON to array. (Important for HTML Table conversion and only pulling columnDefs from config entity.) I'm currently working with ag-Grid support on issue, but xss:filteradmin was added. The additional options section shouldn't have any issues right now due to being handled as plain text.