Dmitrii Krasnov

Put all repositories into `pluginManagement` and `dependencyResolutionManagement`. This approach creates a single place with all available repositories for all projects. Also, for `dependencyResolutionManagement` set a `RepositoriesMode.PREFER_SETTINGS)`, which enables repositories only...

- [x] move plugin and dependency repositories to settings file - [x] change files from `gradle` to gradle convention plugins 1 by 1 - [x] remove usages of `allprojects` block...

Removed allprojects block from root build script

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Gradle docs says that we should avoid [allprojects and subprojects blocks](https://docs.gradle.org/current/userguide/sharing_build_logic_between_subprojects.html#sec:convention_plugins_vs_cross_configuration). In this PR I made next steps: - Moved common logic from `allprojects` block in the root build script...

Moved publishing.gradle to convention plugin

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Divided `publishing.gradle` into two convention plugins: `non-multiplatform.publish-conventions.gradle.kts` and `publish-conventions.gradle.kts` Depends on * https://github.com/Kotlin/kotlinx-atomicfu/pull/434

Moved compile-options.gradle to conventions plugin

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Moved compile `compile-options.gradle` to `compile-options-conventions.gradle.kts` conventions plugin

Enabled https://docs.gradle.org/current/userguide/isolated_projects.html

**Description:** The current build script setup in `integration-testing` module for tests is not clear. It has [some workarounds](https://github.com/Kotlin/kotlinx-atomicfu/blob/dc1c5f5162dd976a9bded61d0d4b967c05d719ae/integration-testing/build.gradle.kts#L32) to work well with idea. **Suggested solution:** Use [JVM Test Suites](https://docs.gradle.org/current/userguide/jvm_test_suite_plugin.html)