[foreign-memaccess+abi] RFR: Improve exception messages and simplify LayoutPath [v7]

[Per Minborg]

On Wed, 20 Sep 2023 13:28:02 GMT, Per Minborg <pminborg at openjdk.org> wrote:

>> 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 three additional commits since the last revision:
> 
>  - Use distinct methods for type check
>  - Revert back to the old reref logic
>  - Remove Stable annotations

src/java.base/share/classes/jdk/internal/foreign/LayoutPath.java line 333:

> 331:         if (!layoutClass.isAssignableFrom(layout.getClass())) {
> 332:             throw badLayoutPath(
> 333:                     String.format("attempting to select a %s element from a non-%s layout: %s (%s)",

While it is good to see the breadcrumbs, having them enclosed in parentheses creates confusion as the layouts themselves contain parentheses as shown in the example below.

Is there a better way (e.g. using `{}`)?


Bad layout path: attempting to select a sequence element from a non-sequence layout: [i4(3a)i4(3b)](2) ([[2:[i4(3a)i4(3b)](2)](1)](0) -> [2:[i4(3a)i4(3b)](2)](1) -> [i4(3a)i4(3b)](2))

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PR Review Comment: https://git.openjdk.org/panama-foreign/pull/886#discussion_r1331632015