Add focus modifier for inputfields

[PavelHolec]

The modifier has a different API than the native one. Ours can be specified only once for the whole screen, using our existing identifier identity. We can later add another modifier mimicking the native one, if needed.

Native:

@FocusState private var focus: FieldType?

TextField(...)
   .focused($focus, equals: .firstname)

TextField(...)
   .focused($focus, equals: .middleName)

TextField(...)
   .focused($focus, equals: .lastname)

Orbit:

VStack(alignment: .leading, spacing: .large) {
    InputField(...)
        .identifier(Input.one)

    InputField(...)
        .identifier(Input.two)

    InputField(...)
        .identifier(Input.three)
}
.inputFieldFocus($focus)

Screen.Recording.2023-08-15.at.10.23.40.mov