[LV] Add initial support for partial alias masking

[MacDue]

This patch adds initial support for partial alias masking, which allows entering the vector loop even when there is aliasing within a single vector iteration. It does this by clamping the VF to the safe distance between pointers. This allows the runtime VF to be anywhere from 2 to the "static" VF.

Conceptually, this transform looks like:

  // `c` and `b` may alias.
  for (int i = 0; i < n; i++) {
    c[i] = a[i] + b[i];
  }

->

  svbool_t alias_mask = loop.dependence.war.mask(b, c);
  int num_active = num_active_lanes(mask);
  if (num_active >= 2) {
    for (int i = 0; i < n; i += num_active) {
      // ... vector loop masked with `alias_mask`
    }
  }
  // ... scalar tail

Alias masking can be used both with/without tail folding, however has the current patch as a few limitations:

• Currently, the mask and transform is only valid for IC = 1
  • Some recipes may not handle the "ClampedVF" correctly at IC > 1
  • Note: On AArch64, we also only have native alias mask instructions for IC = 1
• Reverse iteration is not supported
  • The mask reversal logic is not correct for the alias mask (or clamped ALM)
• This style of vectorization is not enabled by default/costed
  • It can be enabled with -force-partial-aliasing-vectorization
  • When enabled, alias masking is used instead of the standard diff checks (when legal to do so)

This PR supersedes #100579 (closes #100579).