[foreign-memaccess+abi] RFR: Change classes into records and fix finality [v2]

[Per Minborg]

> This PR converts some of the regular classes into records. It also fixes some finality issues.
> 
> Note: Some methods with a very long method parameter list have their parameter list broken up into separate lines.

Per Minborg has updated the pull request incrementally with one additional commit since the last revision:

  Revert changes to VMStorage

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Changes:
  - all: https://git.openjdk.org/panama-foreign/pull/725/files
  - new: https://git.openjdk.org/panama-foreign/pull/725/files/c96b9397..ee8c2014

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=panama-foreign&pr=725&range=01
 - incr: https://webrevs.openjdk.org/?repo=panama-foreign&pr=725&range=00-01

  Stats: 66 lines in 1 file changed: 50 ins; 0 del; 16 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/725.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/725/head:pull/725

PR: https://git.openjdk.org/panama-foreign/pull/725