Add `mlirModuleFromOperation` to C API

At the moment `MlirModule`s can be converted to `MlirOperation`s, but not
the other way around (at least not without going around the C API). This
makes it impossible to e.g. run passes over a `ModuleOp` created through
`mlirOperationCreate`.

Reviewed By: nicolasvasilache, mehdi_amini

Differential Revision: https://reviews.llvm.org/D102497