Previously, the builtin BigIntToWasmI64 and its calling descriptor had
an inconsistent name, not reflecting the signature which is i64 to BigInt.

This CL removes BigIntToWasmI64 in favor of I64ToBigInt. Also for
consistency the Wasm tranpoline has been renamed from BigIntToWasmI64
to WasmI64ToBigInt.

Change-Id: I4125ee99a7358797181770f413db70affa657d5c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1532065
Auto-Submit: Sven Sauleau <ssauleau@igalia.com>
Commit-Queue: Andreas Haas <ahaas@chromium.org>
Reviewed-by: Andreas Haas <ahaas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60361}