Enable JVM IR for stdlib/reflect/test libraries

Changes in Gradle integration tests are needed because:
- in new-mpp-android, kotlin-stdlib-jdk8 is used, and JVM IR generates
  JDK 8-specific bytecode (invokedynamic). D8 needs to be configured to
  desugar it with source/target versions set to 1.8, otherwise it
  reports an error.
- in AndroidExtensionsManyVariants and AndroidIcepickProject, D8 fails
  with assertions enabled if AGP < 4.0.0 is used because of
  https://issuetracker.google.com/issues/148661132. The tests which use
  old AGP versions are probably not relevant anymore anyway.

Changes in kotlin-stdlib-runtime-merged.txt are caused by a slightly
different generation scheme of collection subclasses in JVM IR, and are
harmless.

(Previous attempt was at 15e978dbd311c2ba78ec32b394c21acde9811ccb.)

gradle.properties

@@ -7,9 +7,6 @@ org.gradle.java.installations.fromEnv=JDK_16,JDK_17,JDK_18,JDK_9,JDK_10,JDK_11,J
 cacheRedirectorEnabled=true
 defaultSnapshotVersion=1.6.255-SNAPSHOT
 
-# Enable JVM IR backend for kotlin-stdlib, kotlin-reflect, kotlin-test.
-#kotlin.build.useIRForLibraries=true
-
 #maven.repository.mirror=http://repository.jetbrains.com/remote-repos/
 #bootstrap.kotlin.repo=https://maven.pkg.jetbrains.space/kotlin/p/kotlin/bootstrap
 #bootstrap.kotlin.version=1.1.50-dev-1451