[SR-5110] Name collision not solved with namespacing

[swift-ci]

Previous ID	SR-5110
Radar	https://bugreport.apple.com/web/?problemID=32590357
Original Reporter	Quintana (JIRA User)
Type	Bug
Status	Resolved
Resolution	Duplicate

Environment

Xcode 9 beta 1

Additional Detail from JIRA

Votes	1
Component/s	Compiler
Labels	Bug
Assignee	None
Priority	Medium

md5: 18451fab6884f0b95388b0d7b3e5d5d0

duplicates:

• SR-898 Unresolvable "ambiguous for type lookup" error when using multiple modules

Issue Description:

Having a name collision in Xcode 9/Swift 3.2 is not solved by prefixing the module name in some cases.

I have a iOS project that has a dependency named `Decodable` which has a protocol you could adopt named the same way. Since Swift 3.2 also added a protocol name `Decodable`, there's a name collision.

I instantly thought of namespacing the protocol conformace to remove the error. But it did not work.

```
class MyClass: Decodable -> class MyClass: Decodable.Decodable
```

However, namespacing with `Swift`, does work, but does not solve the issue

```
class MyClass: Decodable -> class MyClass: Swift.Decodable
```

[belkadan]

Consolidating.