Add eclipselsp jdt:// support for textDocument/definition (#4030)

This patch adds support for opening jdt:// links on "go to definition" requests returned by Java language servers.

Co-authored-by: w0rp <devw0rp@gmail.com>

test/lsp/test_lsp_startup.vader

@@ -138,7 +138,7 @@ Before:
       \     'id': 1,
       \     'params': {
       \       'initializationOptions': {},
-      \       'rootUri': ale#path#ToURI(a:root),
+      \       'rootUri': ale#path#ToFileURI(a:root),
       \       'rootPath': a:root,
       \       'processId': getpid(),
       \       'capabilities': {
@@ -253,7 +253,7 @@ Before:
       \     'jsonrpc': '2.0',
       \     'params': {
       \       'textDocument': {
-      \         'uri': ale#path#ToURI(expand('#' . a:buffer . ':p')),
+      \         'uri': ale#path#ToFileURI(expand('#' . a:buffer . ':p')),
       \         'version': ale#lsp#message#GetNextVersionID() - 1,
       \         'languageId': a:language,
       \         'text': "\n",