PR #10297: [NVIDIA GPU] Unroll all nested loops for double buffering transformer
PR #10297: [NVIDIA GPU] Unroll all nested loops for double buffering transformer

Imported from GitHub PR https://github.com/openxla/xla/pull/10297

The loop_double_buffer_transformer pass currently only unrolls the loops in the main computation.
There are some cases where the memcpies(which this pass is designed to eliminate) would exist in nested loops.
This pr changes the pass to look at all loops in the module include the nested ones and unroll them.
Copybara import of the project:

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af8c7b1944d14f5268809c5eb0e71166411ddb19 by TJ <tjx@nvidia.com>:

Unroll all nested loops for double buffering transformer

Merging this change closes #10297

FUTURE_COPYBARA_INTEGRATE_REVIEW=https://github.com/openxla/xla/pull/10297 from Tixxx:tixxx/enable_double_buffer_nested af8c7b1944d14f5268809c5eb0e71166411ddb19
