x/tools/gopls: include function literals as outgoing callhierarchy calls

[leitzler]

What version of Go are you using (go version)?

$ go version
go version devel +6d2b3351f6 Thu Dec 10 18:34:40 2020 +0000 darwin/amd64
x/tools: 929a8494

What did you do?

Called callHierarchy/outgoingCalls from func fn():

package foo
func fn() { // Listing Outgoing calls at "fn" here returns none
	func() {
		fn2()
	}()
}
func fn2() {}

What did you expect to see?

I expected to get one result; the function literal at the line below.
The main reason is for consistency, since calling callHierarchy/incomingCalls from func fn2() will return the function literal.

What did you see instead?

No outgoing calls from fn().