RFR: 8327835: Convert java/awt/FileDialog/RegexpFilterTest/RegexpFilterTest applet test to main [v3]

[Alexander Zvegintsev]

> The `java/awt/FileDialog/RegexpFilterTest/RegexpFilterTest` test is written to test the very specific functionality of `XFileDialogPeer`, so it shouldn't be run on platforms other than Linux.
> 
> We also need to set `sun.awt.disableGtkFileDialogs` to `true` to be able to test `XFileDialogPeer`, because by default it tries to use the Gtk file dialog if it is available.
> The Gtk file dialog has a search field hidden under the magnifying glass icon, but it has a different syntax.
> 
> The Windows system file dialog allows you to use wildcard filtering in the "File name" field by hitting the `enter` afterwards, but again, this test was written to test our own file dialog implementation, not the system's.

Alexander Zvegintsev has updated the pull request incrementally with one additional commit since the last revision:

  review comments

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Changes:
  - all: https://git.openjdk.org/jdk/pull/18203/files
  - new: https://git.openjdk.org/jdk/pull/18203/files/b43ce26b..e1b9422e

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=18203&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=18203&range=01-02

  Stats: 14 lines in 1 file changed: 1 ins; 0 del; 13 mod
  Patch: https://git.openjdk.org/jdk/pull/18203.diff
  Fetch: git fetch https://git.openjdk.org/jdk.git pull/18203/head:pull/18203

PR: https://git.openjdk.org/jdk/pull/18203