[js/web] JSEP Gather OP (#16855)
### Description
Added Gather op that works with both i32 and i64 indices, assuming that
values fall into i32 limit. The assumption is safe because it's not
possible to allocate more than 2gb buffer for inputs.
It treats all data from input tensor as u32, copying 1 or 2 elements for
i64, u64 and double.
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Co-authored-by: Guenther Schmuelling <guschmue@microsoft.com>
