[jdk11u-dev] RFR: 8306135: Clean up and open source some AWT tests

[Andrew Lu]

I backport this for parity with 11.0.21-oracle.

test/jdk/java/awt/Dialog/DialogAsParentOfFileDialog.java
'!errors.isEmpty()' is modified to 'errors.length() > 0' as 'isEmpty()' is not supported in 11.

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Commit messages:
 - Backport 4ad3ac6317f6fc95fdf0340885d4099e785132ad

Changes: https://git.openjdk.org/jdk11u-dev/pull/2113/files
 Webrev: https://webrevs.openjdk.org/?repo=jdk11u-dev&pr=2113&range=00
  Issue: https://bugs.openjdk.org/browse/JDK-8306135
  Stats: 360 lines in 3 files changed: 360 ins; 0 del; 0 mod
  Patch: https://git.openjdk.org/jdk11u-dev/pull/2113.diff
  Fetch: git fetch https://git.openjdk.org/jdk11u-dev.git pull/2113/head:pull/2113

PR: https://git.openjdk.org/jdk11u-dev/pull/2113