Introduce TListBox.AutoScrollWidth property

Original Reporter info from Mantis: Vladimir

• Reporter name: Vladimir Zhirov

Description:

Since Delphi compatible TListBox.ScrollWidth property is inconvenient to use (see issue #18912 (closed) for more details), I suggest adding new boolean TListBox.AutoScrollWidth property, that would automatically adjust horizontal scrollbar.

Implementation for LCL-Win32 can be based on the patch for issue #18912 (closed). LCL-GTK/LCL-Qt implementation details can be clarified by the actual commit that was done to resolve that issue (r30138).

Providing a patch is in my plans but unfortunately I cannot do it in short term, so:
* feel free to postpone this feature request to any Lazarus target,
* feel free to take over.

Mantis conversion info:

• Mantis ID: 19079
• Version: 0.9.31 (SVN)
• Fixed in version: 2.1 (SVN)
• Fixed in revision: 65169 (#8a96677e)