[REQ] [swift] Make typealias optional, as swiftUseApiNamespace isn't as useful otherwise

Is your feature request related to a problem? Please describe.

The value of swiftUseApiNamespace seems to be immediately revoked because each model has a typealias created which pulls the namespaced value into the module namespace.

I'm using internal, namespaced, read-only models - but at the top of each file I get this:

internal typealias Foobar = MyNamespace.Foobar

I discovered these because when I pulled these generated source files into a project, my project failed to compile due to one of the models clashing with a domain entity.

Describe the solution you'd like

I would like an option for making the typealias optional (enabled by default when using namespaces). Something like:

swiftUseTypealias - Flag for generating a typealias in the module's namespace when swiftUseApiNamespace=true, in order to lift the API class out of the {{projectName}}API inner-class.

Examples (swiftUseApiNamespace=true)

// swiftUseTypealias=true

@available(*, deprecated, renamed: "MyNamespace.Foobar")
internal typealias Foobar = MyNamespace.Foobar

extension MyNamespace {

internal struct Foobar: Codable {
...

// swiftUseTypealias=false

extension MyNamespace {

internal struct Foobar: Codable {
...

Start by locating the Swift generator handling for swiftUseApiNamespace and the generated typealias shown in the issue. Trace how generator options reach the Swift templates, then identify the relevant generation tests; done means the typealias can be disabled while namespaced models still generate correctly.