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.)

libraries/stdlib/jdk7/build.gradle

@@ -90,8 +90,6 @@ compileTestKotlin {
     ]
 }
 
-configureJvmIrBackend(project)
-
 LibrariesCommon.configureJava9Compilation(project, 'kotlin.stdlib.jdk7')
 
 task testJdk6Tests(type: Test) {

libraries/stdlib/jdk8/build.gradle

@@ -75,8 +75,6 @@ compileTestKotlin {
     ]
 }
 
-configureJvmIrBackend(project)
-
 LibrariesCommon.configureJava9Compilation(project, 'kotlin.stdlib.jdk8')
 
 task testJdk6Tests(type: Test) { thisTask ->

libraries/stdlib/jvm/build.gradle

@@ -143,8 +143,6 @@ compileLongRunningTestKotlin {
     kotlinOptions.freeCompilerArgs += "-Xopt-in=kotlin.ExperimentalStdlibApi"
 }
 
-configureJvmIrBackend(project)
-
 task longRunningTest(type: Test, dependsOn: longRunningTestClasses) {
     group = "verification"
     testClassesDirs = sourceSets.longRunningTest.output.classesDirs