[Byecode] Hide internal Kotlin fields marked with @JvmField.

[jpobst]

Fixes #954

Internal Kotlin fields that are marked with @JvmField are exposed as public in the compiled bytecode so they can be consumed by Java.

// Kotlin
@JvmField
internal val city: String = "London"

// Java
@JvmField
@NotNull
public final String city = "London";

This is a bit of a conundrum because internal means "can't be consumed by other libraries" and @JvmField means "make this consumable by other Java libraries". 🤷‍♂️

This can cause issues for binding, as the type of those fields may be internal, and thus our binding process will not find the type.

Let's honor the original internal visibility to produce consistent bindings. (kotlin-internal can be overridden with generator metadata if desired.)

We need to examine the encoded Kotlin metadata to determine if the field should be marked as kotlin-internal the same way we do with methods and properties.