RFR: 8313408: Use SVG for BoxLayout example

[Alexey Ivanov]

Replace the GIF image of `BoxLayout` example with an SVG one which renders crisp on all the displays, including High DPI ones.

Compare the images:

  * [`BoxLayout`](https://docs.oracle.com/en/java/javase/17/docs/api/java.desktop/javax/swing/BoxLayout.html#class-description), Java 17, with GIF image;
  * [`BoxLayout`](https://cr.openjdk.org/~aivanov/8313408//api/java.desktop/javax/swing/BoxLayout.html#class-description) with SVG image.

(The updated version lacks CSS and JS from the javadoc tool; there are only two files `BoxLayout.html` and `BoxLayout-1.svg`.)

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Commit messages:
 - 8313408: Use SVG for BoxLayout example

Changes: https://git.openjdk.org/jdk/pull/15169/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=15169&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8313408
  Stats: 77 lines in 3 files changed: 74 ins; 0 del; 3 mod
  Patch: https://git.openjdk.org/jdk/pull/15169.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15169/head:pull/15169

PR: https://git.openjdk.org/jdk/pull/15169