Add support for extended constant pool arrays.

This CL adds support for ConstantPoolArrays which contain an extended section.
This will be used to enable larger constant pools than can be addressed by a
single ldr with immediate offset instruction (which has a limit of a 4KB range).
Extended constant pools will have a small section, which is addressable via a
single ldr instruction, and an extended section, which will require a multi-
instruction sequence to load from.

Currently, no code uses the extended ConstantPoolArray's - this change will
be made in a followup CL.

A number of changes are made to the ConstantPoolArray object in order to
support this:
  - Small section layout is now entirely defined by the small layout bitmaps.
  - The ConstantPoolArray no longer extends FixedArrayBase since the length
    field is not useful for extended layouts.
  - Enums are used to represent the type of an entry and the layout section.
  - An iterator can be used to iterate through all elements of a given type.
  - A number of tests were added for these features.

R=ulan@chromium.org

Review URL: https://codereview.chromium.org/304143002

git-svn-id: https://v8.googlecode.com/svn/branches/bleeding_edge@21653 ce2b1a6d-e550-0410-aec6-3dcde31c8c00