refactor: create hasScripts util

[SethFalco]

I'd like for SVGO to have more utilities, so we can have more consistent behavior between plugins and simplify the plugins themselves.

One clear pick was determining if a node contained scripts, which was done differently across several plugins. This creates a utility that takes from existing checks, and adds more.

A node that meets one of the following conditions is treated as one that contains scripts:

• If there is a <script> tag that contains text.
• If there is a <a> tag with a JavaScript URI.
• If there is an event attribute.

Related

• More context on the individual checks in fix(removeScriptElement): remove link anchors with scripts #1807