Optimizing: Better invoke-static/-direct dispatch.

Add framework for different types of loading ArtMethod*
and code pointer retrieval. Implement invoke-static and
invoke-direct calls the same way as Quick. Document the
dispatch kinds in HInvokeStaticOrDirect's new enumerations
MethodLoadKind and CodePtrLocation.

PC-relative loads from dex cache arrays are used only for
x86-64 and arm64. The implementation for other architectures
will be done in separate CLs.

Change-Id: I468ca4d422dbd14748e1ba6b45289f0d31734d94