[foreign-memaccess+abi] RFR: Improve exception messages and simplify LayoutPath [v4]

[Per Minborg]

> This PR proposes to improve the exception messages in the internal `LayoutPath` class and also do some code simplifications.

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

  Update src/java.base/share/classes/jdk/internal/foreign/LayoutPath.java
  
  Co-authored-by: Jorn Vernee <JornVernee at users.noreply.github.com>

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

Changes:
  - all: https://git.openjdk.org/panama-foreign/pull/886/files
  - new: https://git.openjdk.org/panama-foreign/pull/886/files/fcb7532c..a4c26f69

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=panama-foreign&pr=886&range=03
 - incr: https://webrevs.openjdk.org/?repo=panama-foreign&pr=886&range=02-03

  Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/886.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign.git pull/886/head:pull/886

PR: https://git.openjdk.org/panama-foreign/pull/886