| A menu for window creation in the workbench.
An OpenPerspectiveMenu is used to populate a menu with
actions that will open a new perspective. If the user selects one of
these items either a new page is added to the workbench, a new
workbench window is created with the chosen perspective or the current
perspective will be replaced with the new onw.
The visible perspectives within the menu may also be updated dynamically to
reflect user preference.
The input for the page is determined by the value of pageInput.
The input should be passed into the constructor of this class or set using
the setPageInput method.
This class may be instantiated; it is not intended to be subclassed.
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