Request to bump LSP4J version 0.20.1 to 0.21.0

[cherylking]

The 0.21.0 version removes a dependency on org.eclipse.xtend.lib which thereby removes a transitive dependency on guava. There's a new CVE related to guava which is why I am interested in this getting changed.

[angelozerr]

@cherylking there is a PR for that at #1529 and I suggest you that you read comments and add your comments.

The main problem with lsp4j 0.21.0 is that it requires to change java version and it is very annoying for vscode xml users even if we have binary.

More I dont see the value to use this last version of lsp4j about features. It will be difficult to explain to vscode users that it requires new version of java altough it doesnt provide new features

[cherylking]

@angelozerr Thanks for the pointer. We are already requiring Java 17 for all of our IDE tools. So I don't think that will be a problem for us, but I will keep an eye on that PR and the various comments.