RFR: 6777156: GTK L&F: JFileChooser can jump beyond root directory in combobox and selection textarea. [v3]

[Abhishek Kumar]

> When a user selects ../ from directory list in GTK FileChooser continuosly, it leads to '../../../.....' in combobox and selection textarea even though it the current directory is at root level.
> 
> Fix for the issue is to check if current directory is root then don't process the selection of ' ../ '.
> 
> Test case has been added and checked in CI pipeline. Link is attached in JBS.

Abhishek Kumar has updated the pull request incrementally with one additional commit since the last revision:

  Review comment fix and test case changed to manual

-------------

Changes:
  - all: https://git.openjdk.org/jdk/pull/10390/files
  - new: https://git.openjdk.org/jdk/pull/10390/files/ff3bce2c..698a1202

Webrevs:
 - full: https://webrevs.openjdk.org/?repo=jdk&pr=10390&range=02
 - incr: https://webrevs.openjdk.org/?repo=jdk&pr=10390&range=01-02

  Stats: 98 lines in 2 files changed: 29 ins; 55 del; 14 mod
  Patch: https://git.openjdk.org/jdk/pull/10390.diff
  Fetch: git fetch https://git.openjdk.org/jdk pull/10390/head:pull/10390

PR: https://git.openjdk.org/jdk/pull/10390