Add a special case for append() arguments so we infer the expected
type from the append() context. For example:
var foo []int
foo = append(<>)
We now infer the expected type at <> to be []int. We also support the
variadicity of append().
Change-Id: Ie0ef0007907fcb7992f9697cb90970ce4d9a66b8
Reviewed-on: https://go-review.googlesource.com/c/tools/+/205606
Run-TryBot: Rebecca Stambler <rstambler@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Rebecca Stambler <rstambler@golang.org>
