Reworked joint build (kotlin + kotlin-ultimate)

- Root buildscript classpath no more depends on buildSrc.jar from kotlin-ultimate. This allows to have stable joint builds - w/o occasional "Unresolved reference" errors in buildscripts.
- kotlin-ultimate modules are now included into Kotlin project when two conditions are met: 1) Gradle parameter 'cidrPluginsEnabled' is turned on; 2) kotlin-ultimate Git repo is checked out right to the Kotlin project root (assuming there is 'kotlin-ultimate' directory inside the project root).

build.gradle.kts

@@ -34,15 +34,6 @@ buildscript {
         classpath(kotlin("gradle-plugin", bootstrapKotlinVersion))
         classpath("net.sf.proguard:proguard-gradle:6.1.0")
         classpath("org.jetbrains.dokka:dokka-gradle-plugin:0.9.17")
-
-        // a workaround to add another one buildSrc with Cidr-specific tools to Gradle classpath
-        val kotlinUltimateBuildSrcDep = "org.jetbrains.kotlin.ultimate:buildSrc:1.0"
-        if (findProperty("cidrPluginsEnabled")?.toString()?.toBoolean() == true) {
-            logger.info("Adding buildscript classpath dependency \"$kotlinUltimateBuildSrcDep\" in build.gradle.kts")
-            classpath(kotlinUltimateBuildSrcDep)
-        } else {
-            logger.info("NOT adding buildscript classpath dependency \"$kotlinUltimateBuildSrcDep\" in build.gradle.kts")
-        }
     }
 }