RFR: 8316003: Update FileChooserSymLinkTest.java to HTML instructions [v3]

[Alexey Ivanov]

> To demonstrate the functionality of HTML formatting in `PassFailJFrame`, I updated the instructions for the `test/jdk/javax/swing/JFileChooser/FileChooserSymLinkTest.java` test. The commands to create the symbolic links are marked up with monospace font, which makes them stand out. The test instructions for single- and multi-selection are emphasised with bold text.
> 
> This change depends on #15660 and [JDK-8294158](https://bugs.openjdk.org/browse/JDK-8294158).

Alexey Ivanov has updated the pull request incrementally with one additional commit since the last revision:

  Amend indentation of nested <li> elements

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Changes:
  - all: https://git.openjdk.org/jdk/pull/15661/files
  - new: https://git.openjdk.org/jdk/pull/15661/files/41eaf1b8..a8339019

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=15661&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=15661&range=01-02

  Stats: 18 lines in 1 file changed: 0 ins; 0 del; 18 mod
  Patch: https://git.openjdk.org/jdk/pull/15661.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/15661/head:pull/15661

PR: https://git.openjdk.org/jdk/pull/15661