Pull Request for Issue #10070 .

Based on idea by @RoterNagel about using viewport units for modals, and the proposal of @andrepereiradasilva to create special classes for viewport units.

This PR is full B/C as this one is not changing current behavior. It adds new optional options modalWidth and bodyHeight to be able to set viewport units in the modal constructor.
Note: for old browsers with no viewport unit support, it will just displayed the modal as before.

The Options for modals are then these ones:

• title (string) : The modal title
• backdrop (mixed) : A boolean select if a modal-backdrop element should be included (default = true) The string 'static' includes a backdrop which doesn't close the modal on click.
• keyboard (boolean) : Closes the modal when escape key is pressed (default = true)
• closeButton (boolean) : Display modal close button (default = true)
• animation (boolean) : Fade in from the top of the page (default = true)
• footer (string) : Optional markup for the modal footer
• url (string) : URL of a resource to be inserted as an iframe inside the modal body
• height (string) : height of the iframe containing the remote resource
• width (string) : width of the iframe containing the remote resource
• NEW bodyHeight (int) : Optional height of the modal body in viewport units (vh)
• NEW modalWidth (int) : Optional width of the modal in viewport units (vh)

Summary of Changes

• Changes done on latest Staging (to get the previous modal changes already merged in 3.6.0-dev)
• New modal options: modalWidth and bodyHeight
• Add jviewport classes to modals.joomla.less
• Update responsive-767px-max.joomla.less
• Run generatecss
• Integrate new options in the modal layouts (with control for a correct vh value)
• Add those 2 new options in the menuTypeModal for test and demonstrate B/C

Note: i added viewport options here only for Menu Item Type select for testing purpose. If this PR is accepted, i will then be able to add this to other modals (already updated and merged, and the ones i'm working on and not yet improved). My goal is all modals reviewed for 3.6.0 ;-)

Testing Instructions

• Apply patch on latest staging
• Clean cache (to clean template.css in cache)
• Go to menus > new menu item > click to select a Menu Item Type
• Verify that now the modal is higher (bodyHeight 70vh) as expected in PR #10070
• Note: I have set modalWidth to 80vw as the default modal width was already 80% (and in this modal menu-type, seems to be a good width)

Before Patch

After Patch

• Test other modals (Batch, Messaging > Settings, ...) to confirm B/C, and nothing change for other modals where modalWidth and bodyHeight not specified.