[9] RFR (S) 8050173: Generalize BMH.copyWith API to all method handles

[Vladimir Ivanov]

http://cr.openjdk.java.net/~vlivanov/8050173/webrev.00/
https://bugs.openjdk.java.net/browse/JDK-8050173

Added j.l.i.MethodHandle.copyWith(MethodType, LambdaForm) and provided 
implementation for all subclasses.

Also, some cleanups:
   * rewrote MH.viewAsType on top of MH.copyWith;
   * extended MH.viewAsType to do strict checks w/ assertions turned on 
(new parameter: boolean strict);
   * extended MT.isViewableAs to accept both interface preserving and 
interface erasing conversions (new parameter: boolean keepInterfaces).

Testing: jdk/java/lang/invoke, jdk/java/util/streams, nashorn, octane w/ 
"-ea -esa" and COMPILE_THRESHOLD={0,30}.

Reviewed-by: vlivanov, ?
Contributed-by: john.r.rose at oracle.com

Thanks!

Best regards,
Vladimir Ivanov