RFR: 8338728: Misc issues in memory layout javadoc [v2]

[Maurizio Cimadamore]

> This PR fixes two minor issues in the `MemoryLayout` javadoc:
> * the section describing dereference path talks about `P` and `P'` but then only uses `P` in the code;
> * the `ceilDiv` math on the `PathElement::sequenceElement(long, long)` is wrong, as the division returns a negative number for F < 0, which is incorrect

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

  * Clarify javadoc for var handles with dereference path elements
  * Add test where dereference path element is last element in path

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Changes:
  - all: https://git.openjdk.org/jdk/pull/20659/files
  - new: https://git.openjdk.org/jdk/pull/20659/files/8a8b0c7b..8079981b

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=20659&range=01
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=20659&range=00-01

  Stats: 29 lines in 2 files changed: 25 ins; 0 del; 4 mod
  Patch: https://git.openjdk.org/jdk/pull/20659.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/20659/head:pull/20659

PR: https://git.openjdk.org/jdk/pull/20659