Add support for failing build when multiple types are mapped to the same type

[jrosen081]

Closes #176

Adds validation to the configurations created to make sure that two types are not mapped to the same type in the same module. The output looks as following:

Error: The following Java classes were mapped to the same Swift type:
  Swift Type: Testing.ProcessBuilder, Java Types: java.lang.Math, java.lang.ProcessBuilder

The configuration used was:

{
  "classes": {
    "java.lang.ProcessBuilder": "ProcessBuilder",
    "java.lang.Math": "ProcessBuilder"
  }
}

[ktoso]

Suggested change

	"Swift Type: \(mapping.swiftType.swiftModule ?? "").\(mapping.swiftType.swiftType), Java Types: \(mapping.javaTypes.sorted().joined(separator: ", "))"
	"Swift Type: '\(mapping.swiftType.swiftModule ?? "")'.\(mapping.swiftType.swiftType), Java Types: \(mapping.javaTypes.sorted().map({ "'\($0)'" })joined(separator: ", "))"

I'd split out the creating of the names into separate lines, this is a bit busy inside the string interpolation

[jrosen081]

updated and made a helper function to split it out even more

[ktoso]

Minor nit but looks good :-)

[DougGregor]

Thank you!