layoutlib: use ASM 6.0

This moves us closer to support for v53 class files (OpenJDK 9). These are
not currently created (by default) in the Android platform build process,
but once they are, they will require ASM 6.0 to parse.

For <= v52 class files, use of ASM 6.0 vs. 5.2 should make no difference.

This CL also updates the instructions from Main.java, which referred to
what looks like pre-Android N names.

Bug: 38177569
Test: Treehugger
Test: In a working environment with EXPERIMENTAL_USE_OPENJDK9
      and with numerous unsubmitted changes in other git projects,
      "make checkbuild" works after but not before this CL.
Test: In the same working environment, the following doesn't crash:
      make layoutlib && java -jar \
      out/host/linux-x86/framework/layoutlib_create.jar \
      out/host/common/obj/JAVA_LIBRARIES/temp_layoutlib_intermediates/javalib.jar \
      out/target/common/obj/JAVA_LIBRARIES/core-libart_intermediates/classes.jar \
      out/target/common/obj/JAVA_LIBRARIES/core-oj_intermediates/classes.jar \
      out/target/common/obj/JAVA_LIBRARIES/framework_intermediates/classes.jar

Change-Id: I313aedbaea46e3c4eeedcf6fb1bac982caea38fc