Missing escaping when creating import of existing Go module

[robin-aws]

Description

See test for what this fixes: without this fix we end up with an import on the consumer side that says import Math ".../Math" when the correct name is Math_.

How has this been tested?

Augmented the timesTwo.dfy separate compilation test.

By submitting this pull request, I confirm that my contribution is made under the terms of the MIT license.

[MikaelMayer]

The issue in the generated code of this one is that it used to be

	if _System.Companion_Nat_.Is_(_3_x) {

but now it is

	if Companion_Nat_.Is_(_3_x) {

I see other change slike:

func (*NT) String() string {
	return "_module.NT"
}

into

func (*NT) String() string {
	return "_System.NT"
}

[MikaelMayer]

I fixed the issue with the CI. I'm not sure why the original PR was doing both the escaping and setting ModuleName globally. I'm not sure as well what test to write?

[MikaelMayer]

Nice test !