perf(v-safe-html): Remove a small inefficiency in the directive's node clearing algorithm

What does this MR do?

Remove a loop to unset content in the DOM node, and opting instead for setting the node's textContent to an empty string.

It's relatively slow to loop over each DOM node and remove them one-by-one.

The Fixes

el.textContent = '' is identical in practice to the loop that removes each node one-by-one.

Why

We (the groupcode review team) noticed a significant performance decrease when many parts of the DOM use v-safe-html.

While this change may not induce us to return to using that directive, it will likely improve performance in other parts of the app.

Does this MR meet the acceptance criteria?

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