[dfsan] Add empty APIs for field-level shadow

This is a child diff of D92261.

This diff adds APIs that return shadow type/value/zero from origin
objects. For the time being these APIs simply returns primitive
shadow type/value/zero. The following diff will be implementing the
conversion.

As D92261 explains, some cases still use primitive shadow during
the incremential changes. The cases include
1) alloca/load/store
2) custom function IO
3) vectors
At the cases this diff does not use the new APIs, but uses primitive
shadow objects explicitly.

Reviewed-by: morehouse

Differential Revision: https://reviews.llvm.org/D92629