Use registered FIR compiler extensions in Analysis API.

This will allow IDE plugins to contribute compiler plugins to analysis,
above and beyond those used for the actual compilation step. These
plugins can be used to, for example, provide declarations for code that
is generated during build by an external tool.

^KT-57763 fixed

analysis/project-structure/src/org/jetbrains/kotlin/analysis/project/structure/KtCompilerPluginsProvider.kt

@@ -13,6 +13,8 @@ import org.jetbrains.kotlin.extensions.ProjectExtensionDescriptor
 public abstract class KtCompilerPluginsProvider {
     /**
      * Returns a list of extensions of a base [extensionType] which are registered for [module]
+     *
+     * These extensions are used in addition to those provided by the extension descriptor's [ProjectExtensionDescriptor.getInstances].
      */
     public abstract fun <T : Any> getRegisteredExtensions(module: KtSourceModule, extensionType: ProjectExtensionDescriptor<T>): List<T>
 }