Set apiVersion and languageVersion to 2.0 for backwards compatibility

[hugoncosta]

Following the discussion in square/okhttp#9032 and the PR in square/okhttp#9040, the purpose of this change is to ensure Okio remains compatible with Kotlin 2.0.

My change is only within the Okio package - to make the entire project compatible, there would need to be a few changes in other modules, more specifically adapting the usage of the new Kotlin Clock (see https://github.com/search?q=repo%3Asquare%2Fokio%20kotlin.time.Clock&type=code).

[hugoncosta]

Similar to the OkHttp PR mentioned above, limiting the scope of this change by only ensuring that the source sets remain compatible with Kotlin 2.0 - tests, which are already using 2.1+ features (like the new Clock and Instant) can remain on the latest version.

[Goooler]

Suggested change

	// Some sourceSets do not end with Test, easier to use the negative
	matching { !it.name.endsWith("Test") }.all {
	// Setting these to allow for backwards compatibility
	languageSettings {
	apiVersion = "2.0"
	languageVersion = "2.0"
	}
	}
	tasks.withType<KotlinCompile>().configureEach {
	if (name.contains("test")) return@configureEach // Skip test source sets.
	compilerOptions {
	// Pin language level to 2.0 to ensure compatibility with older Gradle versions and other libraries that depend on okhttp.
	// https://docs.gradle.org/current/userguide/compatibility.html#kotlin
	languageVersion = org.jetbrains.kotlin.gradle.dsl.KotlinVersion.KOTLIN_2_0
	apiVersion = org.jetbrains.kotlin.gradle.dsl.KotlinVersion.KOTLIN_2_0
	}
	}

[yschimke]

This caused some issues committing to the OkHttp PR

square/okhttp#9040

[omarismail94]

You probably also want to set the coreLibrariesVersion field in the kotlin extension to 2.0.21 Something like:

  afterEvaluate {
    extensions.getByType(KotlinProjectExtension::class.java)
      .coreLibrariesVersion = "2.0.21"
  }