{ImportedFunctionEntry} offers two {set} methods: One takes a
{JSReceiver*}, the other one a {WasmInstanceObject*}. Since
{WasmInstanceObject} inherits from {JSReceiver}, it's quite easy to
confuse the two if the instance is hold as e.g. {JSObject}.
Hence, rename the methods to remove this ambiguity.

R=titzer@chromium.org

Bug: v8:7758
Change-Id: I06617a565faa561d3afc70085e0df3b528c715bb
Reviewed-on: https://chromium-review.googlesource.com/1059147Reviewed-by: Ben Titzer <titzer@chromium.org>
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Cr-Commit-Position: refs/heads/master@{#53185}