Fix Import collisions (take default imports into an account)

[elb3k]

Name collision fixes do not take into account default imports here.

Sample input:

sort/sort.proto:

syntax = "proto3";
option go_package = "com.sort;sort";
package com.sort;

enum Enum {
  ENUM = 0;
}

sample.proto:

syntax = "proto3";

option go_package = "com.sample";
package com.sample;

import "validate/validate.proto";
import "sort/sort.proto";

message Message{
    sort.Enum enum = 1;
}

Output:

sample.pb.validate.go:

...

// ensure the imports are used
var (
	_ = bytes.MinRead
	_ = errors.New("")
	_ = fmt.Print
	_ = utf8.UTFMax
	_ = (*regexp.Regexp)(nil)
	_ = (*strings.Reader)(nil)
	_ = net.IPv4len
	_ = time.Duration(0)
	_ = (*url.URL)(nil)
	_ = (*mail.Address)(nil)
	_ = anypb.Any{}
	_ = sort.Sort

	_ = sort.Enum(0)
)
...

which should have been:

...

// ensure the imports are used
var (
	_ = bytes.MinRead
	_ = errors.New("")
	_ = fmt.Print
	_ = utf8.UTFMax
	_ = (*regexp.Regexp)(nil)
	_ = (*strings.Reader)(nil)
	_ = net.IPv4len
	_ = time.Duration(0)
	_ = (*url.URL)(nil)
	_ = (*mail.Address)(nil)
	_ = anypb.Any{}
	_ = sort.Sort

	_ = sort1.Enum(0)
)
...

[CLAassistant]

All committers have signed the CLA.

[elliotmjackson]

Thanks for another great addition @elb3k! Can you add a test case to the harness so that we can ensure this doesn't regress?

[elb3k]

Thanks for another great addition @elb3k! Can you add a test case to the harness so that we can ensure this doesn't regress?

Done. Not sure if this is the best way to test it.