refactor Kotlin extensions

[MukjepScarlet]

1. Make them hide to Java
2. Make them inline for better performance

[Icosider]

For the second point: This won't have any effect, as inline was added to embed code instead of a lambda. Lookt at Kotlin inline the first part.

Inlining may cause the generated code to grow. However, if you do it in a reasonable way (avoiding inlining large functions), it will pay off in performance, especially at "megamorphic" call-sites inside loops.

[MukjepScarlet]

inline makes sense to:

1. Kotlin FunctionN types
2. Simple enough (basically a redirect or alias)

e.g. (stdlib)

@SinceKotlin("1.1")
@kotlin.internal.InlineOnly
public actual inline fun maxOf(a: Int, b: Int): Int {
    return Math.max(a, b)
}

You can search @Suppress("NOTHING_TO_INLINE") on GitHub. Up to now there are 13k code result, including: okio, kotlinx-datetime and many other libs.

[Astralchroma]

When used like this inline basically replaces the inline function call with the function the inline function is calling internally, it basically operates as an alias. It won't increase binary size.

The actual performance increase from this is likely very low or none at all, the JVM is probably smart enough to inline both function calls anyway, the most this will do is speed things up a little bit until JIT kicks in.

It's not a bad change, but it's not likely to yield any improvement.

[MukjepScarlet]

Another purpose is to avoid auto completion like Matrix4fKt to Java code.