Simple stack traces are captured through Isolate::CaptureSimpleStackTrace.
Captured frames are stored in a FixedArray, which in turn is stored as a
property (using a private symbol) on the error object itself. Actual formatting
of the textual stack trace is done lazily when the user reads the stack
property of the error object.

This would involve many conversions back and forth between index-encoded raw
data (receiver, function, offset and code), JS CallSite objects, and C++
CallSite objects.

This commit refactors the C++ CallSite class into a Struct class called
StackTraceFrame, which is the new single point of truth frame information.
Isolate::CaptureSimpleStackTrace stores an array of StackTraceFrames, and JS
CallSite objects (now created only when the user specifies custom stack trace
formatting through Error.prepareStackTrace) internally only store a reference
to a StackTraceFrame.

BUG=

Review-Url: https://codereview.chromium.org/2230953002
Cr-Commit-Position: refs/heads/master@{#38645}