Error when mock generating dot import file with different package name

[eyasy1217]

Actual behavior If your source file contains dot imports and the output package name is different, mockgen's output will be a file that cannot be compiled.

Expected behavior The output will be a file that can be compiled successfully.

To Reproduce

1. The source file internal.go, which contains a dot import, is as follows:

   
   package internal

//go:generate go run go.uber.org/mock/mockgen -source=internal.go -destination=mocks/internal_gen.go

import ( . "context" )

type WithDotImports interface { ImportDot() Context }

2. Run `go generate ./...`. This produces the file `mocks/internal_gen.go`.

3. In `mocks/internal_gen.go`, the return type `Context` of the `ImportDot` method is incorrectly qualified as `internal.Context`, even though such qualification is unnecessary.
```go
package mock_internal

import (
    . "context"
    // ...
)

// ...

func (m *MockWithDotImports) ImportDot() internal.Context {
    m.ctrl.T.Helper()
    ret := m.ctrl.Call(m, "ImportDot")
    ret0, _ := ret[0].(internal.Context)
    return ret0
}

Additional Information

• gomock mode (reflect or source): source (I haven't tried withe reflect, issue might also happen)
• gomock version or git ref: v0.4.0
• golang version: 1.21.3

Triage Notes for the Maintainers

Dot import are seldom used. This bug may not be worth fixing. So how about adding the following code to after this line.

    if pkg.Name != outputPackageName && len(pkg.DotImports) > 0 {
        log.Fatalf("Different package name specifications including dot imports are not yet supported: %v != %v", pkg.Name, outputPackageName)
    }

Fundamentally, the issue seems to be that parseType method in mockgen/parse.go does not return the correct package name for dot import types.