TYPO3 Core

There was a long settings for years:
window.open(top.WorkspaceFrontendPreviewEnabled?'" .
- $urlPreviewDisabled . "':'" . $urlPreviewEnabled

you see that it's turned around.

But reference is wrong too. The value resides in
TYPO3.configuration.workspaceFrontendPreviewEnabled

But,
1) this is static, it change when you reload backend.php. Menu is dynamic, so never fits.
2) setting is turned around for obvious reasons

Solution: When using workspace selector, change the setting dynamic. Use the correct var and the correct comparison.
Splitted in inWorkspace and workspaceFrontendPreviewEnabled, so the workspace preview is enabled only if you are in any workspace and have the preview enabled.

(issue imported from #M14097)