[Themes] Automatic theme for light/dark

- Eclipse's ThemeEngine will try to automatically set the light or dark theme on startup if the themeid setting is not present in the org.eclipse.e4.ui.css.swt.theme.prefs file or that file doesn't exist (fresh workspace)

- We'll expose this in Preferences as a new automatic pseudo theme. This will delete the themeid setting so that the auto theming occurs on startup

Fix FormatPainter not copying image

- Copy the image bytes into FormatPainterInfo
- See #1075

[ACLI] Better error message when model not loaded

[GEF] Workaround connection line dash spacing bug on Windows 200% sca…

…le part 2

- copyLineAttributes should be called *after* our workaround

- If a diagram node contains an image this will mean that graphics.pushState() and graphics.popState() are called again and the line dash is big

[Help] Update help documentation and screenshots for new features

[GitHub] Maven 3.9.4

Revert path to Java on macOS so Help menu works again

- This needs to be ../jre/lib/libjli.dylib on earlier versions of macOS
- See #927

Eclipse 4.27

- Update pom and target to 4.27 and 2023-03

- Help no longer needs org.eclipse.jdt.core.compiler.batch as a dependency as this is part of Eclipse now

Set osgi.requiredJavaVersion=17

[Themes] Update themes

- swt-shadow-visible: false is not needed after Eclipse 4.25
- Note - from Eclipse 4.25 onwards, the "System" theme has been removed. Perhaps we should deprecate our copy?