internal/lsp: enable semantic tokens as part of all experiments

Let's start testing semantic tokens in the Go Nightly extension.

Change-Id: I0c5b1f0891d1e55f876bde1bf8c81feca97fb57b
Reviewed-on: https://go-review.googlesource.com/c/tools/+/288652
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/source/options.go

@@ -672,7 +672,7 @@ func (o *Options) AddStaticcheckAnalyzer(a *analysis.Analyzer) {
 // features offered by gopls. Any experimental features specified in maps
 // should be enabled in enableAllExperimentMaps.
 func (o *Options) enableAllExperiments() {
-	// There are currently no experimental features in development.
+	o.SemanticTokens = true
 }
 
 func (o *Options) enableAllExperimentMaps() {