Feature request: expose escaping information

[empijei]

As of Go 1.14 escape analysis info can be outputted as json: https://golang.org/doc/go1.14#compiler

Please consider adding a setting to expose this information in vim-go.

Running the compiler with go build -gcflags="-m -l -json 0,out" the/package will give useful machine readable info on potential optimization points.

[bhcleek]

Closing, because this is effectively a duplicate of #2039