[foreign-memaccess+abi] RFR: 8291639: Improve the ability to visualize a MemorySegment in human readable forms [v4]

[Per-Åke Minborg]

> This PR imrproves the ability to visualize a `MemorySegment` in human-readable forms.
> 
> It exposes two new methods by adding them directly to the MemorySegment interface. There are other ways to add the methods (e.g. by exposing them via a utility class).
> 
> The methods
> 
> 
>     /**
>      * Returns a Stream of human-readable, lines with hexadecimal values for this memory segment.
>      * <p>
>      * The exact format of the stream elements is unspecified and should not
>      * be acted upon programmatically. Loosely speaking, this method renders
>      * a format similar to the *nix command "hexdump -C".
>      * <p>
>      * As an example, a memory segment created, initialized and used as follows
>      * {@snippet lang = java:
>      * MemorySegment memorySegment = memorySession.allocate(64 + 4);
>      * memorySegment.setUtf8String(0, "The quick brown fox jumped over the lazy dog\nSecond line\t:here");
>      * memorySegment.hexStream()
>      *     .forEach(System.out::println);
>      *}
>      * might print to something like this:
>      * {@snippet lang = text:
>      * 0000000000000000  54 68 65 20 71 75 69 63  6B 20 62 72 6F 77 6E 20  |The quick brown |
>      * 0000000000000010  66 6F 78 20 6A 75 6D 70  65 64 20 6F 76 65 72 20  |fox jumped over |
>      * 0000000000000020  74 68 65 20 6C 61 7A 79  20 64 6F 67 0A 53 65 63  |the lazy dog.Sec|
>      * 0000000000000030  6F 6E 64 20 6C 69 6E 65  09 3A 68 65 72 65 00 00  |ond line.:here..|
>      * 0000000000000040  00 00 00 00                                       |....|
>      *}
>      * <p>
>      * Use a {@linkplain MemorySegment#asSlice(long, long) slice} to inspect a specific region
>      * of a memory segment.
>      *
>      * @return a Stream of human-readable, lines with hexadecimal values
>      */
>      default Stream<String> hexStream() {
>         return MemorySegmentRenderUtil.hexStream(this);
>     }
> ``` 
> 
> and
> 
> 
>     /**
>      * Returns a human-readable view of this memory segment viewed through
>      * the provided memory layout {@code lens}.
>      * <p>
>      * Lines are separated with the system-dependent line separator {@link System#lineSeparator() }.
>      * Otherwise, the exact format of the returned view is unspecified and should not
>      * be acted upon programmatically.
>      * <p>
>      * As an example, a memory segment viewed though the following memory layout lens
>      * {@snippet lang = java:
>      * var lens = MemoryLayout.structLayout(
>      *         ValueLayout.JAVA_INT.withName("x"),
>      *         ValueLayout.JAVA_INT.withName("y")
>      * ).withName("Point");
>      *}
>      * might be rendered to something like this:
>      * {@snippet lang = text:
>      * Point {
>      *   x=1,
>      *   y=2
>      * }
>      *}
>      * <p>
>      * This method is intended to view memory segments through small and medium-sized memory layout
>      * lenses and is, in all cases, restricted by the inherent String capacity limit.
>      *
>      * @param lens  to use as a lens when viewing the memory segment
>      * @return a view of the memory segment viewed through a memory layout lens
>      * @throws OutOfMemoryError if the view exceeds the array size VM limit
>      */
>     default String viewThrough(MemoryLayout lens) {
>         Objects.requireNonNull(lens);
>         return MemorySegmentRenderUtil.viewThrough(this, lens);
>     }

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

  Fix failing test and rename variables

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

Changes:
  - all: https://git.openjdk.org/panama-foreign/pull/695/files
  - new: https://git.openjdk.org/panama-foreign/pull/695/files/62f3fbbc..6690cd8e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=panama-foreign&pr=695&range=03
 - incr: https://webrevs.openjdk.org/?repo=panama-foreign&pr=695&range=02-03

  Stats: 71 lines in 3 files changed: 9 ins; 2 del; 60 mod
  Patch: https://git.openjdk.org/panama-foreign/pull/695.diff
  Fetch: git fetch https://git.openjdk.org/panama-foreign pull/695/head:pull/695

PR: https://git.openjdk.org/panama-foreign/pull/695