float based enums are generated as int

[ArcturusZhang]

Describe the issue or request

See here:

autorest.csharp/test/UnbrandedProjects/Unbranded-TypeSpec/src/Generated/Models/FloatExtensibleEnum.cs

Line 17 in d444259

public FloatExtensibleEnum(int value)

Its corresponding tsp:

@doc("Float based extensible enum")
union FloatExtensibleEnum {
    float32,
    One: 1.0,
    Two: 2.0,
    Four: 4.0,
}