JVM: Add D8 check that class files can be dexed with D8.

This change adds D8 in addition to Dx which is being deprecated.
At some point after the official Dx deprecation, we should remove
the Dx checker.

Moving to D8 has the additional benefit that D8 can dex code
using java 8 features without using a separate desugaring tool.

compiler/testData/codegen/box/classes/quotedClassName.kt

@@ -1,6 +1,11 @@
 // IGNORE_BACKEND: JS_IR
 // IGNORE_BACKEND: JS
 
+// Exclamation marks are not valid in names in the dex file format.
+// Therefore, do not attemp to dex this file as it will fail.
+// See: https://source.android.com/devices/tech/dalvik/dex-format#simplename
+// IGNORE_DEXING
+
 class `A!u00A0`() {
     val ok = "OK"
 }

compiler/testData/codegen/box/localClasses/nameWithWhitespace.kt

@@ -1,6 +1,14 @@
 // IGNORE_BACKEND: JS_IR
 // IGNORE_BACKEND: JS
 
+// Names with spaces are not valid according to the dex specification
+// before DEX version 040. Therefore, do not attempt to dex the resulting
+// class file. When D8 is updated to the most recent version, we can increase
+// the min android api level during dexing to allow these spaces.
+//
+// See: https://source.android.com/devices/tech/dalvik/dex-format#simplename
+// IGNORE_DEXING
+
 fun `method with spaces`(): String {
     data class C(val s: String = "OK")
     return C().s