Replace remark-java

[datho7561]

The fork of remark-java that we use has been archived by the maintainer. Look into alternative libraries to accomplish the same thing.

See:

• Bump jsoup from 1.14.2 to 1.15.3 in /org.eclipse.lemminx #1288 (we need to update a library to address a security vulnerability, but updating the library breaks remark-java)
• https://github.com/kotcrab/remark-java
• com.kotcrab.remark:remark will be archived eclipse-jdtls/eclipse.jdt.ls#2214

[rgrunber]

As you mentioned, we can't use flexmark-java because it requires a Java 11 runtime. Is there any chance we can upstream a fix to revert to Java 8 (at least in the html-to-markdown module) in addition to the jsoup version bump ? I got the impression they only started using Java 11 everywhere for fixing some test issues : vsch/flexmark-java#494 (comment)