RFR: 8317819: Scope should reflect lifetime of underying resource (mainline)

[Maurizio Cimadamore]

This PR is based on a port of: openjdk/panama-foreign#898

Some additional changes are contained in this PR:

* instead of using a different "always alive" scope for zero-length memory segments, we now use the global scope
* the javadoc for `MemorySegment::ofArray`, `MemorySegment::ofBuffer` and `SymbolLookup::loaderLookup` is tweaked to say that the scope associated to the returned segments is an automatic scope
* the javadoc for `MemorySegment.Scope` defines the concepts of global and automatic scope, which are then referenced in the `Arena` javadoc.

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Commit messages:
 - Initial push

Changes: https://git.openjdk.org/jdk/pull/16183/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=16183&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8317819
  Stats: 147 lines in 11 files changed: 83 ins; 15 del; 49 mod
  Patch: https://git.openjdk.org/jdk/pull/16183.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/16183/head:pull/16183

PR: https://git.openjdk.org/jdk/pull/16183