[docs-framework] Rewrite custom remark plugins & Fix private API dependencies

[nicolethoen]

1a. Rewrite remove-comments.js (Effort: Small)

Currently 22 lines, uses this.Parser.prototype.blockTokenizers + eat() to strip HTML
comments
Migration: Likely redundant — parseMD.js already does remove(tree, 'comment') later in the
pipeline. May be able to just delete it.
1b. Rewrite auto-link-url.js (Effort: Small-Medium)

Currently 33 lines, re-adds https://... autolink support that remark-mdx strips
Migration: Check if remark-mdx v3 still strips autolinks. If not, this plugin is
unnecessary. If still needed, convert to an MDAST tree transform or write a micromark
extension.

2a. Fix mdx-hast-to-jsx.js (Effort: Medium)

Uses remark-mdx/lib/serialize/ private internals for serializeTags() and
serializeMdxExpression()
Uses hast-to-hyperscript and @mdx-js/util (v1) which may not exist in v3
Uses this.Compiler pattern (removed in unified v11)
Need to find public API replacements or inline the functionality
2b. Fix mdx-ast-to-mdx-hast.js (Effort: Small-Medium)

Uses mdast-util-to-hast/lib/all private import
Handler API may differ in mdast-util-to-hast v13

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Jira Issue: PF-3695