Tests: Improved detection of empty patterns

[RunDevelopment]

This improves the static analysis we do using regexp-ast-analysis (= my project that powers some of the static analysis in eslint-plugin-regexp).

I also simplified the logic around lookbehind groups.

[github-actions]

JS File Size Changes (gzipped)

A total of 2 files have changed, with a combined diff of +2 B (+0.1%).

file	master	pull	size diff	% diff
components/prism-asciidoc.min.js	1.62 KB	1.62 KB	+2 B	+0.1%
components/prism-promql.min.js	648 B	648 B	0 Bytes	0%

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