Although every Primitive is a Data, the Cast operations for the
subclasses of Primitive do not allow casting directly from Data to the
subclasses without first going through Value.  Because of this,
Primitives extracted from a V8::FixedArray require two casts to get to
the "real" type.

Thus, as a convenience to embedders, this change makes it possible to
cast directly from Data to all the subtypes of Primitive.

Also, this change makes the parameter names in the declarations match
those in the definitions, though there does not seem to be a universally
followed convention regarding these.

Bug: v8:10958
Change-Id: I18dc3fbb9a9bccb2cb3b75efd829af64d46d8eb9
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2573816Reviewed-by: Marja Hölttä <marja@chromium.org>
Reviewed-by: Camillo Bruni <cbruni@chromium.org>
Commit-Queue: Dan Clark <daniec@microsoft.com>
Cr-Commit-Position: refs/heads/master@{#71649}