Allow all ArrayBufferView types as Buffers

Right now, many modules allow the use of plain Uint8Arrays in addition to Buffers. This PR begins the work to expand such support to all ArrayBufferView types (including all TypedArray types and DataView).

This work was inspired by https://github.com/nodejs/node/issues/1826, which requests support for ArrayBuffer as well. But ArrayBuffer is treated separately from its views in V8's API and it is easier to get started with the work here.

The first two commits add the necessary infrastructure for consuming and testing all ArrayBufferView types. The last two demonstrate how to update the JS layer for it. (Specifically, using the new isArrayBufferView utility function and update usage of buf.length to buf.byteLength).

I don't intend this PR to make its way into 8.0.0.

Relevant discussions on IRC with @addaleax

2017-03-23 20:20:54 TimothyGu  So I was looking at https://github.com/nodejs/node/issues/1826
2017-03-23 20:21:23 TimothyGu  As we are trying to support Uint8Array in C++ binding it doesn't
                               look much more work to support all the other ArrayBufferView types
2017-03-23 20:21:40 TimothyGu  including all TypedArray and DataView
2017-03-23 20:21:54 addaleax   right … that was also pointed out to me in the last streams wg
                               meeting
2017-03-23 20:22:32 addaleax   I understand where it’s coming from, but so far I have wanted to
                               keep the changes pretty minimal
2017-03-23 20:23:06 addaleax   bc going from Buffer support to Uint8Array support is, for the most
                               part, a tiny change
2017-03-23 20:23:27 addaleax   if somebody (you?) wants to work on this, yay
2017-03-23 20:23:40 TimothyGu  TBH it doesn't take much of a change on the C++ side to get it
                               working
2017-03-23 20:23:46 TimothyGu  http://sprunge.us/SgET
2017-03-23 20:23:54 TimothyGu  or http://sprunge.us/SgET?diff
2017-03-23 20:25:12 TimothyGu  so I thought maybe we could just support all of them at the same
                               time
2017-03-23 20:25:25 addaleax   that’s nice, yes
...
2017-03-23 20:28:20 addaleax   re: generic ArrayBufferView support … the one reason I’ve not been
                               doing that is that my personal goal is to give users a more
                               standard way of passing in binary data, and Uint8Arrays work just
                               fine for that purpose. the other reason is that there is at least a
                               small bit of ambiguity, because interpreting e.g. a Uint16Array as
                               a Uint8Array can be done in two ways (entry-for-entry or via the...
2017-03-23 20:28:21 addaleax   ...underlying storage)

Checklist

• make -j4 test (UNIX), or vcbuild test (Windows) passes
• tests and/or benchmarks are included
• documentation is changed or added
• commit message follows commit guidelines

Affected core subsystem(s)