[Nestmates] RFR: 8187768 and 8189940 - nest host resolution and exceptions

[David Holmes]

Combined webrev: http://cr.openjdk.java.net/~dholmes/8187768/webrev/

bug: https://bugs.openjdk.java.net/browse/JDK-8187768

8187768: [Nestmates] Improve exception information related to 
bad/missing nest-host class

This work implements the latest specification proposal for nest-host 
resolution and validation exceptions:

http://cr.openjdk.java.net/~dlsmith/nestmates.html

and also provides better diagnostic information for the exceptions that 
occur. Key features:

- instanceKlass::nest_host():
   - passes through most resolution related exceptions
   - replaces NoClassDefFoundError with a  new NCDFE with the original 
as the cause and a message "Unable to load nest-host class of %s" to 
give context to the exception
   - throws IllegalAccessError when nest membership validation fails (as 
per updated spec) with appropriate error message
- Reflection::verify_field_access can now more obviously result in 
pending exceptions
- All callers of Reflection::verify_field_access watch for pending 
exceptions and don't replace them with their own IllegalAccessErrors.
- runtime/Nestmates/membership tests have been completely rewritten to 
test updated spec - including the need to test for failures in the 
calling class's nest-host resolution and in the target class's nest-host 
resolution.

While working here I rediscovered the Xcomp problem where the JIT tries 
to load a nest-host class when not allowed to:

bug: https://bugs.openjdk.java.net/browse/JDK-8189940
8189940:  [Nestmates] VM Compiler thread needs to load nest-host class!

The fix here was to check in InstanceKlass::nest_host() if we are on a 
thread that can't call java, and that we may have to load a nest-host 
class. In that case we return NULL, causing has_nestmate_access_to to 
return false, it's callers post IllegalAccessError and the JIT sees that 
failure and falls back to going through the interpreter to complete its 
work.

runtime/Nestmates tests all pass in normal and Xcomp mode now.

Thanks,
David