[foreign-preview] RFR: 8281855: Rename ResourceScope to MemorySession [v4]

[Maurizio Cimadamore]

> This patch implements some of the changes described in [1] and [2]. More specifically, the `ResourceScope` abstraction is renamed into `MemorySession`, and the session accessors in `MemorySegment`, `NativeSymbol` and `VaList` are tweaked to return *non-closeable* session views. To counteract this change, `MemorySession` now supports `equals` and `hashCode`, so that sessions views can be compared to each other in ways that are not identity-sensitive.
> 
> [1] - https://mail.openjdk.java.net/pipermail/panama-dev/2022-February/016152.html
> [2] - https://mail.openjdk.java.net/pipermail/panama-dev/2022-February/016254.html

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

  Address review comments
  * replace spurious usages of `scope` in direct buffer template

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

Changes:
  - all: https://git.openjdk.java.net/panama-foreign/pull/641/files
  - new: https://git.openjdk.java.net/panama-foreign/pull/641/files/d3a6c44f..2ee6f16b

Webrevs:
 - full: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=641&range=03
 - incr: https://webrevs.openjdk.java.net/?repo=panama-foreign&pr=641&range=02-03

  Stats: 7 lines in 2 files changed: 0 ins; 0 del; 7 mod
  Patch: https://git.openjdk.java.net/panama-foreign/pull/641.diff
  Fetch: git fetch https://git.openjdk.java.net/panama-foreign pull/641/head:pull/641

PR: https://git.openjdk.java.net/panama-foreign/pull/641