Removed allprojects block from root build script

[dkrasnoff]

Gradle docs says that we should avoid allprojects and subprojects blocks.
In this PR I made next steps:

• Moved common logic from allprojects block in the root build script to common-conventions.gradle.kts
• Moved multiplatform connected logic from allprojects block in the root build script to multiplatform-conventions.gradle.kts
• Rewrote to kotlin dsl build script in atomicfu-gradle-plugin

Depends on

• Moved publishing.gradle to convention plugin #435
• Moved compile-options.gradle to conventions plugin #434

[dkrasnoff]

Depends on #435 and #434

[adam-enko]

Great stuff!

[adam-enko]

(I meant to approve before, but I guess I missed the approve button)

A small note: compile-options-conventions.gradle.kts should be converted to a kotlin-base-conventions..gradle.kts and applied in the kotlin-jvm and kotlin-multiplatform conventions. But that can be done in a later PR - I'll leave it up to you.