.gen: rename subdirectory for 1.16 compatibility

[buyology]

Starting from 1.16:

In module mode, the go command now disallows import paths that
include non-ASCII characters or path elements with a leading dot character
(.). Module paths with these characters were already disallowed, […]
so this change affects only paths within module subdirectories.

So attempting to compile packages depending on uber/cadence will fail with:

../../vendor/go.uber.org/cadence/internal/client.go:30:2: malformed import path "go.uber.org/cadence/.gen/go/cadence/workflowserviceclient": leading dot in path element
../../vendor/go.uber.org/cadence/internal/internal_workflow_testsuite.go:39:2: malformed import path "go.uber.org/cadence/.gen/go/cadence/workflowservicetest": leading dot in path element
../../vendor/go.uber.org/cadence/internal/activity.go:29:2: malformed import path "go.uber.org/cadence/.gen/go/shared": leading dot in path element

As per golang/go#43985 (comment):

The only specific affected module we know of so far is go.uber.org/cadence, but because the affected import statement is an internal package it could be fixed for external consumers by an internal-only change within a patch release for that module (namely, moving the packages currently in the .gen subdirectory to another location and updating the imports within the module).

(emphasis added)

[Groxx]

Yea, seems like it's picky all the time. With just eval "$(gimme 1.16)" and:

// main.go
package main
import "go.uber.org/cadence/workflow"
func main() {
    _ = workflow.NewDisconnectedContext()
}

// go.mod
module temp

I get this on go mod tidy (among other failures):

go: downloading golang.org/x/text v0.3.0
temp imports
	go.uber.org/cadence/workflow imports
	go.uber.org/cadence/.gen/go/shared: malformed import path "go.uber.org/cadence/.gen/go/shared": leading dot in path element

so this probably has to be done pretty soon.

[buyology]

Looks like this is going to be relaxed in 1.16.1 after all: golang/go#43985 (comment)

[Groxx]

Excellent. Thank you for the update! I'll wait on these, it'd be better to not force the breakage if we don't have to.

[buyology]

With the recent 1.16.2 release this is no longer an issue. Closing.