swift234

[SDKAnalyzer] The initial commit of swift sdk digester.
This tool takes the input of two versions of the same sdk and outputs
their diff to facilicate the auto-migration of sdk clients.
In this initial commit, we take the path of one sdk and generate
a tree describing its API content. Next, we will diff trees generated
from different versions of the sdk.

In addition, this commit also refactored out part of swift-sdk-analyzer
to the common utils shared with swift-sdk-digester.

Swift SVN r26656