RFC: stop using markdown-it-attrs by default

[d3m1d0v]

Description

There are several important issues when using markdown-it-attrs plugin:

• runtime exception in some cases:
  • runtime error when transform yfm-cut with curly brackets in title transform#375
  • Runtime error in markup with attrs in checklists transform#559
  • Runtime error with tabs markup transform#603
• it is difficult to control the use of attributes in user-generated content

But some of our extensions assume the use of attribute syntax {} and expect attributes to be automatically parsed.

Proposal

I suggest stop using markdown-it-attrs plugin by default in transformer. Extensions should parse attributes for themselves. Utils package already has a custom parser for attributes.

Plan

1. Use AttrsParser from @diplodoc/utils in extensions
2. Add option to transformer to disable markdown-it-attrs plugin
   • enableMarkdownAttrs option with default value true
3. In next transformer major version disable markdown-it-attrs plugin by default