RFR (S): [MVT] Support lambda form customization in LambdaFormBuilder

[Vladimir Ivanov]

http://cr.openjdk.java.net/~vlivanov/valhalla/8184938/webrev.00/

Implement lambda form customization in LambdaFormBuilder. (Duplicated 
logic from InvokerBytecodeGenerator.)

LF customization is crucial for performant MH.invoke() and 
MH.invokeExact() on non-constant method handles. It enables 
JIT-compilers to generate a single nmethod for the whole method handle 
chain.

Otherwise, the method handle chain scatters into numerous nmethods (one 
for each method handle) which severely affects performance (especially 
for MVT where Q-typed lambda forms can't be compiled as a root.)

Testing: jdk/test/valhalla/mvt/

Best regards,
Vladimir Ivanov