eclipse-platform/.github#27: Use CTabFolder to improve Dark Theme on Windows

[betamaxbandit]

improve Dark Theme on Windows eclipse-platform/.github#27

Using CTabFolder and CTabItem, instead of TabFolder/TabItem, improves the look when in Dark Theme; the background of the tab no longer has a non-dark background.

This relates to multiple commits to fix:

[Windows][Dark theme] Multiple preference pages use tab widgets, that are not dark theme aware eclipse-platform/.github#27

[betamaxbandit]

To Test:

1. Launch an eclipse workbench.
2. Create a Java project and provide a project name, use defaults for rest of settings and click Finish.
3. In Preferences > General > Appearance > Theme, choose Dark and click Apply and Close. Restart the workbench when prompted.
4. In Package Explorer, select the project and choose Project > Properties.
5. In the left hand side navigator, select Java Build Path.
   Expected: the Java Build Path page is displayed and tabs (eg: Source, Projects, Libraries, etc) are displayed correctly. The background of the tabs is shown using the Dark Theme colour.
6. Repeat from step 3) and change the Theme to Light.
   Expected: the Java Build Path page is displayed and tabs (eg: Source, Projects, Libraries, etc) are displayed correctly. The background of the tabs is shown using the Light Theme colour.

Before and After screencaptures:

[betamaxbandit]

@jonahgraham

[jonahgraham]

This change looks good to me (and follows the same style as similar changes, like eclipse-platform/eclipse.platform.team#14) - but the metadata needs some updating. The commit message should reference the full path to the issue, i.e. eclipse-platform/.github#27

Note the current message makes a bad cross reference to #27 by having eclipse.jdt.ui eclipse-jdt#27 in it.

Please update the commit message and the summary of the pull request.

[jonahgraham]

Also (as discussed offline) the email address used for the commit needs to be the one associated with your Eclipse Account + ECA so that the ECA validation passes.

[betamaxbandit]

@jjohnstn , thank you for merging.
Cheers John Moule