[scudo][standalone] Add chunk ownership function

Summary:
In order to be compliant with tcmalloc's extension ownership
determination function, we have to expose a function that will
say if a chunk was allocated by us.

As to whether or not this has security consequences: someone
able to call this function repeatedly could use it to determine
secrets (cookie) or craft a valid header. So this should not be
exposed directly to untrusted user input.

Add related tests.

Additionally clang-format caught a few things to change.

Reviewers: hctim, pcc, cferris, eugenis, vitalybuka

Subscribers: JDevlieghere, jfb, #sanitizers, llvm-commits

Tags: #sanitizers, #llvm

Differential Revision: https://reviews.llvm.org/D70908