Show warning banner and disable NewRelic errors for old IE - #16189

This PR fixes two issues:

• Warning banner no longer displays on old-IE browsers (e.g., IE 7, 8)
• NewRelic browser monitor does not correctly filter JS errors thrown by old-IE browsers

The underlying problem is that old-IE browsers throw load errors on webpack-bundled JS, so our unsupported-browser code is never executed correctly in these environments.

This PR refreshes our (unsupported) old-IE browser code so the warning-banner is properly shown and NewRelic error tracking is disabled (tested on IE 7+8).

I've moved the old-IE code into a separate view, and shifted order of operations around to the following sequence:

• load CSS
• load NewRelic-instrumented browser monitoring JS (this is auto-added between theme_common_head_before and theme_common_head_after; PR Manually instrument NewRelic browser monitoring bundle #16158 will explicitly add this in the future
• load old-IE polyfills and execute old-ie javascript (respond.js needs to appear after all CSS, and the NewRelic-error filter needs to appear after NewRelic JS)
• load jQuery (shim calls addEventListener, which needs to come after old-IE polyfills)
• load all other JS (needs to run after old-IE so errors are ignored)