Improve escape_html_attr performance

[mrkishi]

Closes #4016.
Depends on #4015.

Replaces the character-by-character loop with a regex-based str.replace call.

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[benmccann]

can we add a comment about why this is needed?

[PH4NTOMiki]

Why delete < and >
they break HTML if not escaped
we had issue #3773

[PH4NTOMiki]

and we fixed it with #3798 and #3804

[mrkishi]

@PH4NTOMiki That was about escape_json_in_html, this is about escape_html_attr.

@benmccann Sorry about the comments, the previous code didn't have them and I thought they weren't necessary. I'll add some.

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[Rich-Harris]

Nice, I did a naive benchmark locally and this is way faster