Small tweaks to foreign function and memory API

Following integration of the second incubator of the foreign function and memory API (JDK-8275063), we detected few divergences between the contents of the jdk/jdk and panama/foreign-memaccess+abi:

* the name of some of the FunctionDescriptor wither is different, as it has been improved following a change that was not incorporated in (8275063)

* TestUpcall does not execute all the test combinations, because of an issue in the jtreg header (also fixed in foreign-memaccess+abi)

* Addressing some feedback, we would like to bring back VL alignment to JAVA_INT layout constants (and related constants).