🐛 match textarea pattern polyfill against the whole value

[madib06ops]

The textarea pattern polyfill in checkInputValidity compiles the author pattern as new RegExp('^' + pattern + '$', 'm'), which does not match native <input pattern> semantics. The m flag lets ^ and $ match at internal line breaks, and without a non-capturing group a top-level alternation such as cat|dog only anchors one branch, so a value whose first line matches (abc\nanything against [a-z]+) or that merely starts or ends with an alternative passes validation. Compiling as ^(?:pattern)$ with no flags applies the pattern to the whole value the way the browser does.