RFR: 8357799: Improve instructions for JFileChooser/HTMLFileName.java

[Alexey Ivanov]

The instructions for the `javax/swing/JFileChooser/HTMLFileName.java` test are still not as clear.

The file name in the instructions is rendered as HTML, which, I believe, is unexpected. It should be displayed as the plain text.

The instructions also say about file and directory which have HTML in their name; this was true in the initial version of the test in #24439 that created files and directories on the real file system. 

The final version of test uses a virtual file system that displays *three files*, there's no way to navigate.

I also clarified the instructions: look at how the file name of the first file is rendered in _the file pane_ and _the navigation combo box_ (**Look in** in Metal L&F).

In the `VirtualFileSystemView` class, I changed the name of the third file from `virtualFolder` to `virtualFile2.log`, and made the file array a field which ensures `getRoots` and `getFiles` return the same list.


In addition to this, I reduced the number of rows allocated for the instructions. Since the instructions are in HTML format, the number of lines of HTML code makes no sense for determining the size.

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Commit messages:
 - Improve instructions for HTMLFileName.java

Changes: https://git.openjdk.org/jdk/pull/25455/files
  Webrev: https://webrevs.openjdk.org/?repo=jdk&pr=25455&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8357799
  Stats: 43 lines in 1 file changed: 17 ins; 10 del; 16 mod
  Patch: https://git.openjdk.org/jdk/pull/25455.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/25455/head:pull/25455

PR: https://git.openjdk.org/jdk/pull/25455