Fix Tex highlights affecting Markdown with standalone $

[krassowski]

References

Fixes #11482

Code changes

• Adds a regular expression lookahead to the opening conditions for inline tex highlighting.
• Adds visual regression test

User-facing changes

Before:

After:

Backwards-incompatible changes

None

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[fcollonval]

Thanks @krassowski !

[github-actions]

Benchmark report

The execution time (in milliseconds) are grouped by test file, test type and browser.
For each case, the following values are computed: min <- [1st quartile - median - 3rd quartile] -> max.

The mean relative comparison is computed with 95% confidence.

Results table

Test file	large_code_notebook	large_md_notebook
open
chromium
actual	7409 <- [7803 - 8149 - 8322] -> 8661	3577 <- [3766 - 3883 - 4084] -> 4250
expected	7278 <- [7587 - 8057 - 8239] -> 8726	3649 <- [3798 - 4027 - 4125] -> 4423
Mean relative change	1.4% ± 1.2%	-1.5% ± 1.3%
switch-from
chromium
actual	924 <- [984 - 1106 - 1250] -> 1741	582 <- [635 - 857 - 923] -> 1028
expected	861 <- [957 - 1012 - 1201] -> 1606	592 <- [643 - 855 - 923] -> 1111
Mean relative change	5.7% ± 4.5%	-0.5% ± 4.9%
switch-to
chromium
actual	1002 <- [1048 - 1067 - 1081] -> 1245	725 <- [826 - 864 - 891] -> 953
expected	946 <- [1029 - 1047 - 1065] -> 1314	746 <- [822 - 881 - 902] -> 953
Mean relative change	1.7% ± 1.0%	-1.5% ± 1.7%
close
chromium
actual	1042 <- [1142 - 1204 - 1548] -> 1666	672 <- [715 - 731 - 755] -> 880
expected	1013 <- [1110 - 1159 - 1315] -> 1649	666 <- [716 - 729 - 747] -> 876
Mean relative change	6.5% ± 4.6%	0.9% ± 1.3%

Changes are computed with expected as reference.

[fcollonval]

@meeseeksdev please backport to 3.2.x