Consider disallowing backslashes in MyST targets

[hukkin]

Describe the problem/need and solution

Context
In mdit-py-plugins < 0.3 it backslashes were not allowed in MyST targets. Now they are.

Problem / Idea
This is now a valid MyST target:

(myst_target\)=

I think it would be more intuitive and in line with CommonMark if the backslash escape worked, i.e. prevented the target being parsed successfully.

Solution
Disallow backslashes in MyST targets.

Benefit
Consistency with backslashes in CommonMark.

Guide for implementation

No response

Tasks and updates

No response

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[chrisjsewell]

Fair 👍 should be relative easy to make a PR 😉