java.lang.invoke: Add implementation of MethodType.

Imported from OpenJdk8u60. The only significant changes
are that :

- The adapter / lambda-form caches on MethodType / MethodTypeForm
  has been removed because it will not be used on Android.
- Several unused package private methods have been removed.
- Links to MethodHandle API have temporarily been replaced with
  @code markers. They will be resurrected when the MethodHandle
  class is imported.

All changes have been annotated with change markers.

bug: 30550796
test: make checkbuild + MethodTypeTest on host / target.

Change-Id: I6e745d940f5f2949e40ff96fda5f91ba2afa267e
11 files changed