compiler: handle unsafe conversion expression in escape analysis
compiler: handle unsafe conversion expression in escape analysis

Change-Id: I92133973bce0f8c7d4c427c1a04028a33c8a9c30
Reviewed-on: https://go-review.googlesource.com/c/gofrontend/+/192037
Reviewed-by: Than McIntosh <4b2922593166fc595a9b1a408f34f5d3817fe9d2@google.com>
Reviewed-by: Ian Lance Taylor <87e9c6d529889242b7e184afb632328636553ab4@golang.org>

golang/gofrontend,golang/gofrontend,golang/gofrontend,golang/gofrontend