Adjust the placement of LDS writes and reads to immediately follow the
definition of their operands in case where LDS write is in the loop but
it's operand is not. This is a heuristic for optimizing fused attention
by hoisting Q tensor LDS read/write operations outside of the loop, as Q
is a loop invariant and can be loaded once before entering the loop.

In the previous implementation, the heuristic incorrectly assumed that
the operand of the LDS write had to be a load operation, which is
unnecessary. Additionally, there was no explicit check to verify whether
the LDS write was in the loop while its defining operand was not. This
PR addresses both issues.

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Co-authored-by: Ognjen Plavsic <ognjen.plavsic@luxoft.com>