Migrate buildSrc to composite build

[Goooler]

Addressed from #2652.

[Goooler]

• dokka-gradle-plugin project applies convention plugins, need to convert it to a composite build too.
• dokka-gradle-plugin refs some sub-projects in root project, need to declare them in dokka-gradle-plugin's settings.gradle.kts, it also refs some versions outside.

[IgnatBeresnev]

@aSemy could I ask you to take a quick look, please? Maybe you know a way to fix the gradle plugin without copying configuration

[aSemy]

I think converting the Dokka-GP to an included build would be a good step in the future (as well as the integration tests), but it might require a lot of work (e.g. the Worker API), and isn't necessary right now (unless I've missed something @Goooler?).

I think this PR should just set up the bare minimum needed for using included build, and focus on improving the Dokka-GP in another PR. So I think just keep these changes:

• Rename buildSrc to build-logic
• Rename the convention plugins to use the id("org.jetbrains.base") format
• add includeBuild() into the root settings.gradle.kts

And don't update to Gradle 8, and keep Dokka-GP as regular ol' subproject.

WDYT?

[Goooler]

@aSemy Cause dokka-gradle-plugin depends on build-logic, but root project depends on dokka-gradle-plugin.

We'd better to use online version of Dokka in root?

dokka/build.gradle.kts

Lines 4 to 6 in 6fcd66a

	plugins {
	org.jetbrains.conventions.base
	id("org.jetbrains.dokka")

[aSemy]

@aSemy Cause dokka-gradle-plugin depends on build-logic, but root project depends on dokka-gradle-plugin.

We'd better to use online version of Dokka in root?

dokka/build.gradle.kts

Lines 4 to 6 in 6fcd66a

	plugins {
	org.jetbrains.conventions.base
	id("org.jetbrains.dokka")

Ahh right, I see what you mean now.

Yes, I think it's better to use the online version of Dokka. If there's problem in DokkaGP then it could prevent the whole project from compiling during development, which would be annoying.

[IgnatBeresnev]

Well done, thanks! I've triggered integration tests, let's wait for them to pass

[IgnatBeresnev]

Everything looks good 🎉