Implement select element list box with shadow DOM.

LayoutTests/fast/forms/listbox-selection-expected.txt

 <select> selection test for mouse events and keyevents.
 
 On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
 
 
 1) Select one item with mouse (no previous selection)
 PASS selectionPattern("sl1") is "10000"
 2) Select one item with mouse (with previous selection)
 PASS selectionPattern("sl2") is "10000"
 3) Select one item with the keyboard (no previous selection)
@@ skipping 17 matching lines @@
 12) Select an item cmd-clicking
 PASS selectionPattern("sl12") is "01100"
 13) Select a range shift-clicking
 PASS selectionPattern("sl13") is "11110"
 14) Select a range with the keyboard
 PASS selectionPattern("sl14") is "01100"
 PASS successfullyParsed is true
 
 TEST COMPLETE
 
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