This CL adds a bit more rigor to the handling of length properties
in JSObject-derived classes that explicitly contain that property
inline.

This involves:
- Introducing a new superclass of JSArgumentsObject called
  JSArgumentsObjectWithLength that is shared with other object
  instances that also have a fixed length property.
- Adding JSArgumentsObjectWithLength to the type hierarchy in Torque,
  including adding fast-cases for leading the length property for all
  classes deriving from JSObjectWithLength.
- Adding more rigor to Context and NativeContext handling in base.tq.
  This is useful for the map checks required to verify objects are
  argument object types derived from JSArgumentsObjectWithLength.

Change-Id: I2f0a20601ffcb90b3767cbaeb766e9998d3462ec
Reviewed-on: https://chromium-review.googlesource.com/1248661
Commit-Queue: Daniel Clifford <danno@chromium.org>
Reviewed-by: Toon Verwaest <verwaest@chromium.org>
Reviewed-by: Tobias Tebbi <tebbi@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56289}