Support Kotlin context parameters

[atyrin]

The feature still experimental till Kotlin 2.3.
https://github.com/Kotlin/KEEP/blob/context-parameters/proposals/context-parameters.md

Dokka 2.0.0 in K1 and K2 modes ignores the presence of the context parameters in code.

[fzhinkin]

Dokka 2.0.0 in K1 and K2 modes ignores the presence of the context parameters in code.

I'd say things a bit worse: Dokka ignores all the documentation written for functions w/ ctx params and emits an "empty" pages for such functions.

For a declaration like this:

package org.example

/**
 * That's a contextual function!
 *
 * @return nothing.
 */
context(_: Int)
public fun contextual() {
}

you'll get a page like this:

Without a proper support from Dokka, it's unclear how to publish documentation for Stdlib part of the ctx params: https://youtrack.jetbrains.com/issue/KT-72866

[whyoleg]

Initial implementation for context parameters, which is covered by this issue, should support:

1. Showing context parameters in Dokka signatures (functions, properties)

context(a: A, _: B, _: C)
val property: String

context(type: T)
fun <T: CharSequence> withGeneric()

2. Context parameters in lambdas signatures (functions, properties)

fun accept(param: context(X) () -> String)

fun returns(): (context(X) () -> String)

Additional notes:

• Constructors are not allowed to have context parameters (currently)
• Context parameter have no default value (comparing to ordinary parameters)
• Overloads with/without context parameters and with different context parameters

For the next step: #4065