Clarify description of .val( array )

[gibson042]

Ref jquery/jquery#2195

The paragraph on https://api.jquery.com/val/#val-value starting with "Passing an array of element values" is inaccurate, and less clear than it could be. In actuality, we implement two similar but distinct special behaviors for array input, both effectively updating the affected collection to the intersection of provided input with possible values:

• checkbox and radio: check/uncheck based on whether or not their value is in the array
• select elements: select/unselect options based on whether or not their value is in the array

Although jQuery does not directly touch elements outside the context collection, the .val setter can affect them by triggering native behavior restricting to 1 the maximum count of checked radio inputs in a group or selected options in a select-one.