[llvm] [LV][NFC]Preselect folding style before choosing maxing VF, NFC. (PR #81885)

[Alexey Bataev via llvm-commits]

alexey-bataev wrote:

> foldTailByMasking() checks if the default getTailFoldingStyle() is None - implicitly assuming IVUpdateMayOverflow. Worth commenting that checking for None Style can be done independent of IVUpdateMayOverflow, i.e., both styles are None or both of them are not None (right?).

Added TODO comment to check infuture that it is so.

> nit: `selectTailFoldinStyle()` does slightly more than passively "select and record" the style - it also records all masked operations by calling prepareToFoldTailByMasking(), regardless of IVUpdateMayOverflow. And it actually sets two Styles. Perhaps a more accurate name would be `setTailFoldingStyles()`.

Done.

https://github.com/llvm/llvm-project/pull/81885