[GTK] Don't use deprecated gtk_style_context_invalidate()

[SyntevoAlex]

GTK sources say:
Deprecated: 3.12: Style contexts are invalidated automatically.

https://www.eclipse.org/swt/faq.php#gtkstartup says:
Eclipse/SWT 4.16.x: GTK+ 3.20.0 and its dependencies
Eclipse/SWT 4.15.x: GTK+ 3.14.0 and its dependencies

This means that it's been at least 3 years since SWT requires GTK 3.20. Sounds safe to stop using the deprecated function now.

Hopefully fixes #697 I couldn't reproduce it in SWT snippet, so I didn't test this with SWT. But when I tested in native snippet, removing gtk_style_context_invalidate() changed things a bit and crash no longer occurred.

[github-actions]

Test Results

     299 files  ±0       299 suites  ±0   5m 42s ⏱️ +2s
  4 095 tests ±0    4 087 ✔️ ±0    8 💤 ±0  0 ❌ ±0 
12 197 runs  ±0  12 124 ✔️ ±0  73 💤 ±0  0 ❌ ±0 

Results for commit b61252c. ± Comparison against base commit 434d1dd.

♻️ This comment has been updated with latest results.

[SyntevoAlex]

Unfortunately it didn't fix #697.
Still, let's have this code cleanup.
In master now.

[iloveeclipse]

Note: there were no one successful gerrit build for this PR:

This (among other issues) caused errors in building SWT GTK related code, see eclipse-platform/eclipse.platform.releng.aggregator#1608.

I assume version updates are missing for GTK fragments, but I'm not sure. I'm looking into this.

[akurtakov]

https://download.eclipse.org/eclipse/downloads/drops4/I20231129-0600/buildlogs/reporeports/reports/versionChecks.html shows that both swt host and fragments have version updates.

[iloveeclipse]

https://download.eclipse.org/eclipse/downloads/drops4/I20231129-0600/buildlogs/reporeports/reports/versionChecks.html shows that both swt host and fragments have version updates.

OK, the diff shows that bytecode change is related to this PR. The new version is what we actually should use. So if the versions are bumped, why do we have the problem?

[iloveeclipse]

The API errors are reported because classes & sources changed in

• eclipse.platform.swt.binaries/bundles/org.eclipse.swt.gtk.linux.aarch64/pom.xml
• eclipse.platform.swt.binaries/bundles/org.eclipse.swt.gtk.linux.ppc64le/pom.xml
• eclipse.platform.swt.binaries/bundles/org.eclipse.swt.gtk.linux.x86_64/pom.xml

Here the excerpt:

3.  eclipse.platform.swt.binaries/bundles/org.eclipse.swt.gtk.linux.x86_64/pom.xml
   no-classifier: different
      org/eclipse/swt/internal/gtk3/GTK3.class: different
      org/eclipse/swt/widgets/Control.class: different
      org/eclipse/swt/widgets/Display.class: different
      org/eclipse/swt/widgets/Text.class: different
      org/eclipse/swt/widgets/ToolTip.class: different
      org/eclipse/swt/widgets/Tracker.class: different
      org/eclipse/swt/widgets/Widget.class: different
   classifier-sources: different
      library/gtk3.c: different
      library/gtk3_stats.h: different
      org/eclipse/swt/internal/gtk3/GTK3.java: different
      org/eclipse/swt/widgets/Control.java: different
      org/eclipse/swt/widgets/Display.java: different
      org/eclipse/swt/widgets/Text.java: different
      org/eclipse/swt/widgets/ToolTip.java: different
      org/eclipse/swt/widgets/Tracker.java: different
      org/eclipse/swt/widgets/Widget.java: different
    The main artifact has been replaced with the baseline version.
    The following attached artifacts have been replaced with the baseline version: [sources]

[iloveeclipse]

I will now touch the 3 fragments, if that is the way to go.