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

[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);
    }

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

Commit messages:
 - Merge branch 'foreign-memaccess+abi' into render
 - Add rendering of MemorySegments

Changes: https://git.openjdk.org/panama-foreign/pull/695/files
 Webrev: https://webrevs.openjdk.org/?repo=panama-foreign&pr=695&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8291639
  Stats: 666 lines in 4 files changed: 661 ins; 2 del; 3 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