PR #12915: Handle unsigned MLIR integers during FFI attribute conversion
PR #12915: Handle unsigned MLIR integers during FFI attribute conversion

Imported from GitHub PR https://github.com/openxla/xla/pull/12915


Copybara import of the project:

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7a26d6fa5ca122ad3ad56ba9e3668eab8c9b0235 by Andrey Portnoy <aportnoy@nvidia.com>:

Handle unsigned MLIR integers during FFI attribute conversion

Merging this change closes #12915

FUTURE_COPYBARA_INTEGRATE_REVIEW=https://github.com/openxla/xla/pull/12915 from openxla:aportnoy/ffi-attribute-map-handle-unsigned-integers 7a26d6fa5ca122ad3ad56ba9e3668eab8c9b0235
