[MLIR] Move builtin.module LLVM IR translation to before nested operations

This patch moves the call for translating an MLIR module to LLVM IR to the
beginning of the translation process. This enables the use of dialect
attributes attached to `builtin.module` operations and the `amendOperation()`
flow to initialize dialect-specific global configuration before translating
the contents of the module.

Currently, this patch does not impact the generated IR on its own. Testing
infrastructure to allow translating the Test dialect to LLVM IR is added, so
that it can be checked that the current behavior is not broken in the future.

Differential Revision: https://reviews.llvm.org/D158278