Latest restructuring made the 'Add Expression Evaluator'
action to a no-op when not debugging.
Reflect this by disabling the action as long the user is
not debugging and allow complex expressions to be evaluated
for QML as well.
Fixes: QTCREATORBUG-19050
Change-Id: I2d6421a121e2169981b992a617f4d2b7264a8091
Reviewed-by: hjk <hjk@qt.io>