RFR: 8268129: LibraryLookup::ofDefault leaks symbols from loaded libraries [v4]

[Maurizio Cimadamore]

> This patch overhauls the library loading mechanism used by the Foreign Linker API. We realized that, while handy, the *default* lookup abstraction (`LibraryLookup::ofDefault`) was behaving inconsistentlt across platforms.
> 
> This patch replaces `LibraryLookup` with a simpler `SymbolLookup` abstraction, a functional interface. Crucially, `SymbolLookup` does not concern with library loading, only symbol lookup. For this reason, two factories are added:
> 
> * `SymbolLookup::loaderLookup` - which obtains a lookup that can be used to lookup symbols in libraries loaded by current loader
> * `CLinker::systemLookup` - a more stable replacement for the *default* lookup, which looks for symbols in libc.so (or its equivalent in other platforms). The contents of this lookup are unspecified.
> 
> Both factories are *restricted*, so they can only be called when `--enable-native-access` is set.

Maurizio Cimadamore has updated the pull request incrementally with one additional commit since the last revision:

  Address review comments

-------------

Changes:
  - all: https://git.openjdk.java.net/jdk/pull/4316/files
  - new: https://git.openjdk.java.net/jdk/pull/4316/files/41ab74b6..7be87eae

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=4316&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=4316&range=02-03

  Stats: 42 lines in 13 files changed: 6 ins; 6 del; 30 mod
  Patch: https://git.openjdk.java.net/jdk/pull/4316.diff
  Fetch: git fetch https://git.openjdk.java.net/jdk pull/4316/head:pull/4316

PR: https://git.openjdk.java.net/jdk/pull/4316