This fixes point 2 of #20516
This adds a conversion from Dataview/Buffer by returning `obj.buffer`
which can be converted to a `UInt8Array`.
Question: Regarding point 4 of the mentioned issue would it be
appropriate to copy the toU8 helper to the `zlib.mjs` methods?
`opAsync` requires a lookup by name on each async call. This is a
mechanical translation of all opAsync calls to ensureFastOps.
The `opAsync` API on Deno.core will be removed at a later time.
