[Fix emacs-lsp/lsp-ui#452] Fix markdown link navigation in *lsp-help* buffers

[vspinu]

Because markdown links are rendered during fontification I couldn't see where to integrate the link lookup except of the generic lsp--fontlock-with-modelsp--fontlock-with-mode

fixes emacs-lsp/lsp-ui#452

[yyoncho]

CI is not happy: https://github.com/emacs-lsp/lsp-mode/actions/runs/3669045447/jobs/6202594289#step:12:640

[yyoncho]

In toplevel form:
lsp-mode.el:9399:1:Error: the following functions are not known to be defined: text-property-search-forward, prop-match-beginning, prop-match-end
.....................Test lsp-byte-compilation-test backtrace:

[vspinu]

Rewrote. Hopefully it's good now.

[yyoncho]

Looks good, I will do some manual testing I and will proceed with the merge.