<Swing Dev> RFR: 8240690 Race condition between EDT and BasicDirectoryModel.FilesLoader.run0()

[Sergey Bylokhov]

Hello.
Please review the fix for jdk/client.

Bug: https://bugs.openjdk.java.net/browse/JDK-8240690
Fix: http://cr.openjdk.java.net/~serb/8240690/webrev.01

The test in the webrev has failed from time to time in our
CI. It was closed and serialize/deserialize the JFileChooser
on the main thread under Motif L&F only. Initially, I thought
that the intermittent issues will be fixed by moving the code
to EDT. I have done it, and also add a check for all L&Fs.
As a result, I was able to reproduce tons of issues related
to JFileChooser on all platforms.

1. When we create the JFileChooser and initialize some L&F,
we create some background thread that loads the list of files,
and only after that adds the list of files to the JFileChooser
itself. This is one of the exception where we access the swing
component on non EDT, take a look to the changes in
   BasicDirectoryModel.FilesLoader.
I have moved some calls to the JFileChooser from the FilesLoader.run0
which is executed on the background thread to the constructor of
FilesLoader which is executed on the EDT. So on the background
thread, the "JFileChooser.isTraversable" and "JFileChooser.accept" will
be used. These methods are changed to be more multiple-threads
friendly(mostly read the property to the local field then check, then use).

2. During serialization, we temporarily reset the FileSystemView of
the JFileChooser to the null(it is also possible to do this via public API).
This uncovered a few places where we did not expect the null.

3. The "FilesLoader" had a logic of "runnables" blocks of data which
should be used to update the JFileChooser by some portions of data. We
used the only one "runnable" in the Vector of runnables, but even then
it caused a concurrent modification exception if we tried to cancel the
task and background thread modified the list of tasks(the list from empty
became non-empty). ->> I just replaced it by one reference.

Note that this fix works only on top of
https://mail.openjdk.java.net/pipermail/swing-dev/2020-March/010155.html
otherwise serialization just does not work on macOS.

-- 
Best regards, Sergey.