[tint] Loop Analysis: Support `LessThanEqual` operator

This patch adds the support of `LessThanEqual` operator in the
analysis of infinite loop. The loops in one of the below patterns
will be marked as finite ones:

for (var i: T; i <= CONSTANT; i++) {
  // The only other uses of i are loads.
  // CONSTANT is neither i32::kHighestValue (when T is i32) nor
  // u32::kHighestValue (when T is u32)
}

for (var i: T; CONSTANT <= i; i--) {
  // The only other uses of i are loads.
  // CONSTANT is neither i32::kLowestValue (when T is i32) nor
  // u32::kLowestValue (when T is u32)
}

Bug: 401577332
Test: tint_unittests
Change-Id: Iaa52ae4c11c34c0eca5aa648b7a9d300cafa9198
Reviewed-on: https://dawn-review.googlesource.com/c/dawn/+/253654
Commit-Queue: Jiawei Shao <jiawei.shao@intel.com>
Reviewed-by: James Price <jrprice@google.com>