Fix go generate ./... issues under root (#76)

Running `go generate ./...` on current main fails for a couple of
reasons

(1) The go:generate command in
/mockgen/internal/tests/aux_imports_embedded_interface/bugreport.go has
an -aux_file argument that specifies a package `faux` that is not in the
stdlib and therefore not discoverable in GOROOT. Fixing this with a
fully qualified path causes another failure that is known and documented
in mockgen/internal/tests/aux_imports_embedded_interface/README.md.

Because this failure is known, I've opted to comment out the command as
documentation for reproducing the error.

(2) mockgen/internal/tests/internal_pkg/generate.go attempts to mock an
interface package with reflect mode and runs into fundamental go
restrictions of `go build` with internal package paths outside of the
internal package scope allowed by go.

I've removed the generate directive here since this isn't a supported
feature as the implementation of reflect mode creates a tempoorary
directory and invokes `go build` there.

ref:
[reflect.go#L135](github.com/uber-go/mock/blob/8cd1a4cf46a6b1cf232b6862f2f11e81fe77a4e4/mockgen/reflect.go#L135)
ref: [#29](github.com/golang/mock/issues/29)

Not a failure fix but I've also changed type aliases of `any` back to
type aliases of `interface {}`. Looking at the parsing logic,
[parse.go#L752](github.com/uber-go/mock/blob/8cd1a4cf46a6b1cf232b6862f2f11e81fe77a4e4/mockgen/parse.go#L752)
`interface{}` -> `any` causes *ast.TypeSpec to no longer type check to
an *ast.InterfaceType and ends up removing generate mock code meant to
test against regressions.

ref: [#48](github.com//pull/48)

mockgen/internal/tests/aux_imports_embedded_interface/bugreport.go

@@ -1,6 +1,7 @@
 package bugreport
 
-//go:generate mockgen -aux_files faux=faux/faux.go -destination bugreport_mock.go -package bugreport -source=bugreport.go Example
+// Reproduce the issue described in the README.md with
+// $ go:generate mockgen -aux_files faux=faux/faux.go -destination bugreport_mock.go -package bugreport -source=bugreport.go Example
 
 import (
 	"log"

mockgen/internal/tests/copyright_file/input.go

@@ -2,4 +2,4 @@ package empty_interface
 
 //go:generate mockgen -package empty_interface -destination mock.go -source input.go -copyright_file=mock_copyright_header
 
-type Empty any
+type Empty interface{} // migrating interface{} -> any does not resolve to an interface type dropping test generation added in b391ab3

mockgen/internal/tests/empty_interface/input.go

@@ -2,4 +2,4 @@ package empty_interface
 
 //go:generate mockgen -package empty_interface -destination mock.go -source input.go
 
-type Empty any
+type Empty interface{} // migrating interface{} -> any does not resolve to an interface type.

mockgen/internal/tests/internal_pkg/generate.go

@@ -1,4 +1,3 @@
 package test
 
-//go:generate mockgen -destination subdir/internal/pkg/reflect_output/mock.go go.uber.org/mock/mockgen/internal/tests/internal_pkg/subdir/internal/pkg Intf
 //go:generate mockgen -source subdir/internal/pkg/input.go -destination subdir/internal/pkg/source_output/mock.go