This commit introduces several new types:

* JSStackFrame and WasmStackFrame are wrapper classes around a single frame
  in a FrameArray.
* They both inherit from StackFrameBase, which uses virtual dispatch to call
  the correct implementation.
* FrameArrayIterator contains a static instance of JSStackFrame and
  WasmStackFrame and returns a pointer to the corresponding type for each
  frame.
* The JS callsite object now contains the frame array and frame index
  as internal fields.

Internal stack formatting now relies completely on FrameArrayIterator and the
{JS,Wasm}StackFrame types. JS callsite instances are allocated only for custom
user formatting through Error.prepareStackTrace.

BUG=

Review-Url: https://codereview.chromium.org/2275233002
Cr-Commit-Position: refs/heads/master@{#39015}