internal/lsp: use the correct method name to register semantic tokens

Leave the legacy names to handle old versions of the VS Code language
client.

Updates golang/go#42148

Change-Id: Ia3eeef9e792e502c5c8018698b9c0ea3a9b0dfe5
Reviewed-on: https://go-review.googlesource.com/c/tools/+/266479
Trust: Rebecca Stambler <rstambler@golang.org>
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
gopls-CI: kokoro <noreply+kokoro@google.com>
TryBot-Result: Go Bot <gobot@golang.org>
Reviewed-by: Peter Weinberger <pjw@google.com>

internal/lsp/workspace.go

@@ -91,9 +91,15 @@ func (s *Server) didChangeConfiguration(ctx context.Context, _ *protocol.DidChan
 	return nil
 }
 
+// This is a work-around for
+// https://github.com/microsoft/language-server-protocol/issues/1107. Once
+// https://golang.org/cl/266497 has been released for ~1 month, we can probably
+// remove this function and use the only correct method name, which is
+// "textDocument/semanticTokens".
 func semanticTokenRegistrations() []protocol.Registration {
 	var registrations []protocol.Registration
 	for _, method := range []string{
+		"textDocument/semanticTokens",
 		"textDocument/semanticTokens/full",
 		"textDocument/semanticTokens/full/delta",
 		"textDocument/semanticTokens/range",