K2 Support - Add FirDeclarationGenerationExtension as replacement for SyntheticResolveExtension

[cmelchior]

See this Kotlin Slack conversation https://kotlinlang.slack.com/archives/C7L3JB43G/p1691477003733109

But basically, we need to replace our current SyntheticResolveExtension with a similar FirDeclarationGenerationExtension implementation.

With #1476 being merged soon, hopefully, that is the only change that needs to happen.
We still need to rely on ComponentRegistrar rather than CompilerPluginRegistrar due to the issue described here: https://youtrack.jetbrains.com/issue/KT-55300/Provide-a-mechanism-to-describe-ordering-and-dependencies-for-compiler-plugins

See e.g. the all-opens plugin for a strategy on how to create a plugin that supports both: https://github.com/JetBrains/kotlin/tree/master/plugins/allopen