all: replace a few user-visible mentions of golang.org and godoc.org

This change replaces a few user-visible mentions of golang.org and
godoc.org with go.dev and pkg.go.dev, respectively. Non-user-visible
mentions (e.g. in test scripts) were left untouched.

Change-Id: I5d828edcd618b6c55243d0dfcadc6fa1ce9422ce
Reviewed-on: https://go-review.googlesource.com/c/go/+/681255
Reviewed-by: Cherry Mui <cherryyz@google.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@golang.org>
LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com>
Reviewed-by: Dmitri Shuralyov <dmitshur@google.com>

src/cmd/go/internal/bug/bug.go

@@ -69,7 +69,7 @@ const bugFooter = `### What did you do?
 <!--
 If possible, provide a recipe for reproducing the error.
 A complete runnable program is good.
-A link on play.golang.org is best.
+A link on go.dev/play is best.
 -->
 
 

src/cmd/go/internal/cache/default.go

@@ -28,7 +28,7 @@ var initDefaultCacheOnce = sync.OnceValue(initDefaultCache)
 const cacheREADME = `This directory holds cached build artifacts from the Go build system.
 Run "go clean -cache" if the directory is getting too large.
 Run "go clean -fuzzcache" to delete the fuzz cache.
-See golang.org to learn more about Go.
+See go.dev to learn more about Go.
 `
 
 // initDefaultCache does the work of finding the default cache

src/os/exec/exec.go

@@ -17,7 +17,7 @@
 //
 // Note that the examples in this package assume a Unix system.
 // They may not run on Windows, and they do not run in the Go Playground
-// used by golang.org and godoc.org.
+// used by go.dev and pkg.go.dev.
 //
 // # Executables in the current directory
 //