[Polly] Skip vectorize.enable for FP loops with dist=1 dependences (#205756)

When -polly-annotate-metadata-vectorize is active, Polly marks its
generated loops with llvm.loop.vectorize.enable=true. This is harmful
for loops with a loop-carried dependence of distance 1 that involve
floating-point operations: the Loop Vectorizer reorders FP operations
(e.g. scalar reduction like q = factor*q), producing results that differ
from the sequential scalar reference and causing correctness failures.

Two changes are made:

1. IslAst.cpp: add PollyVectorizeMetadata to the PerformParallelTest
gate so that dependence-distance computation is performed whenever
-polly-annotate-metadata-vectorize is passed, not only when
-polly-parallel or a vectorizer is active.

2. IslNodeBuilder.cpp / LoopGenerators.cpp: when a loop has a dist=1
dependence involving FP operations, omit the vectorize.enable annotation
entirely. This lets the Loop Vectorizer apply its own cost model and
legality checks decide.

GitOrigin-RevId: df1838f5d961f9587ca4f90d992bef81cc6155db