Linux GTK4 Snippet #1 "Hello World" Working

Issue #17 covers the larger issue of getting full support for GTK4. This issue is to cover the first step of the order of work.

The first step to getting GTK4 support complete for SWT is getting Snippet1 aka "Hello World" working with GTK4. This means getting the build to work and integrating that into the SWT master branch*.

* or into a branch that is regularly merged with master branch if the SWT committers want to hold off on the merge until some gates are reached, such as merging before M1 or having a more complete implementation.

• task name and Gitlab Issue id,
  • Linux GTK4 Snippet #1 "Hello World" Working
• time estimate, if possible,
  • Unknown
• expected deliverable(s)/outcome(s),
  • A PR or git branch containing the working Snippet1 on GTK4
• identify any dependencies on external resources including Eclipse IT infrastructure updates,
  • The docker images that are used for the build may need to be updated to have the GTK4 dependencies installed. This may require IT support if these changes are not within the control of the SWT project.
• means of demonstration and/or verification of completion.
  • Snippet1 works with GTK4.