This adds the missing support for HOLEY_DOUBLE_ELEMENTS to both
`Array#find()` and `Array#findIndex()`. The implementation just deopts
whenever it hits a double hole. In order to prevent deoptimization
loops we add feedback to the CheckFloat64Hole operator, which also
addresses the TODO in the `%ArrayIteratorPrototype%.next()` lowering.

This provides a speed-up of up to 8x in microbenchmarks when using
`Array#find()` or `Array#findIndex()` on HOLEY_DOUBLE_ELEMENTS arrays.

Bug: chromium:791045, v8:1956, v8:6587, v8:7165, v8:8015
Change-Id: I1be22d3fcba56c676a81dc31a9042f8123ef3a55
Reviewed-on: https://chromium-review.googlesource.com/1183906Reviewed-by: Sigurd Schneider <sigurds@chromium.org>
Commit-Queue: Benedikt Meurer <bmeurer@chromium.org>
Cr-Commit-Position: refs/heads/master@{#55321}