Review Request: JDK-8173978: Lookup.in should allow teleporting from a lookup class in a named module without dropping all access

[Mandy Chung]

This is an enhancement to |`Lookup::in`| and 
|`MethodHandles::privateLookupIn`| API
for cross module teleporting.  A `Lookup` object will record the previous
lookup class from which this |Lookup| object was teleported such that
the access check will use both the previous lookup class and the current
|lookup| context (current lookup class and allowed modes) to determine if
a type is accessible to this `Lookup` object or not.

In a nutshell, `T` in M2 is accessible to a `Lookup` object on `C`
(lookup class in M1) and `PLC` (previous lookup class in M0) if and only if
1. both M0 and M1 can read M2
2. T is in a package that is exported from M2 at least to both M0 and M1

Detailed specification is in Lookup class spec and `accessClass` javadoc.
The relevant spec about cross-module teleporting is in the Lookup class
spec and `Lookup::in` and `MethodHandles::privateLookupIn`.

CSR: https://bugs.openjdk.java.net/browse/JDK-8226916

webrev:
http://cr.openjdk.java.net/~mchung/jdk14/8173978/webrev.00

javadoc:
http://cr.openjdk.java.net/~mchung/jdk14/8173978/javadoc/java.base/java/lang/invoke/MethodHandles.Lookup.html

http://cr.openjdk.java.net/~mchung/jdk14/8173978/javadoc/java.base/java/lang/invoke/MethodHandles.html#privateLookupIn(java.lang.Class,java.lang.invoke.MethodHandles.Lookup)

I have yet to generate the spec diff. The tool is currently broken
due to javadoc change.  I'll try to workaround it and post the
spec diff soon.

thanks
Mandy