[foreign-preview] RFR: 8282873: Bring back SymbolLookup [v3]

[Maurizio Cimadamore]

> This patch brings back the `SymbolLookup` abstraction, which was initially left behind during the move to java.base.
> 
> In hindsight, moving lookup capabilities to `CLinker` and `ClassLoader`, while economical in terms of API surface, is problematic, as it is much harder to users of the API to understand how to look up for library symbols (since lookup capabilities are scattered across different classes).
> 
> Moreover, recent JDK changes, such as JDK-8281335 and JDK-8282608, make library loading more flexible, and much closer to a raw dlopen/dlsym/dlclose. Which means we can now provide, in addition to loader and system lookup, a *third* kind of lookup, which features deterministic library loading/unloading (see `SymbolLoojup::libraryLookup`).
> 
> Overall, I think that having a dedicated abstraction for looking up symbols in libraries is a good thing; not only it makes the API more discoverable, but it also allows clients to define custom lookup (as `SymbolLookup` is a simple functional interface).

Maurizio Cimadamore has updated the pull request incrementally with two additional commits since the last revision:

 - Improve javadoc
 - Add javadoc to clarify role of "name" parameter in libraryLookup factory.

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Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/666/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/666/files/7b5b7273..212dab53

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=666&range=02
 - incr: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=666&range=01-02

  Stats: 2 lines in 1 file changed: 2 ins; 0 del; 0 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/666.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/666/head:pull/666

PR: https://git.openjdk.java.net/panama-foreign/pull/666