RFR: 8230302: GenerateJLIClassesPlugin can generate invalid DirectMethodHandle methods

[Claes Redestad]

Hi,

we currently spin code for a non-sensical invokeVirtual DMH, so let's
remove that.

Such methods are benign since we won't ever attempt to resolve such
nonsensical forms, but surely a waste of space. This patch tightens
checks conservatively (could possibly apply the same restriction to
invokeSpecial?) and adds a few negative tests using inputs that jlink
should refuse.

Webrev: http://cr.openjdk.java.net/~redestad/8230302/webrev.00/

Testing: tier1+2

Thanks!

/Claes