[Bounds checks] Tighten pRange in MergeEdgeAssertions via X != CNS assertions (#121273)

Closes #121259

When we already have, say, `[1..10]` range for `X` and we encounter `X
!= 1` assertion, we can tighten the range to `[2..10]`

Removes bounds checks for the following snippet:
```cs
void Test(ReadOnlySpan<char> name)
{
    if (name is [] or [':'] or [':', not ':', ..])
    {
        Console.WriteLine("test");
    }    
}
```


[Diffs](https://dev.azure.com/dnceng-public/public/_build/results?buildId=1191071&view=ms.vss-build-web.run-extensions-tab)

Author: EgorBo

src/coreclr/jit/rangecheck.cpp

@@ -863,8 +863,28 @@ void RangeCheck::MergeEdgeAssertions(Compiler*        comp,
             }
             else
             {
-                // We have a != assertion, but it doesn't tell us much about the interval. So just skip it.
-                continue;
+                assert(curAssertion->assertionKind == Compiler::OAK_NOT_EQUAL);
+
+                // We have an assertion of the form "X != constLimit".
+                // For example, if the assertion is "X != 100" and the current range for X is [100, X],
+                // we can tighten the range to [101, X].
+                // Similarly, if the range is [Y, 100], we can tighten it to [Y, 99].
+
+                if (pRange->LowerLimit().IsConstant() && pRange->LowerLimit().GetConstant() == cnstLimit)
+                {
+                    limit   = Limit(Limit::keConstant, cnstLimit);
+                    cmpOper = GT_GT;
+                }
+                else if (pRange->UpperLimit().IsConstant() && pRange->UpperLimit().GetConstant() == cnstLimit)
+                {
+                    limit   = Limit(Limit::keConstant, cnstLimit);
+                    cmpOper = GT_LT;
+                }
+                else
+                {
+                    // We can't make any useful deduction from this assertion.
+                    continue;
+                }
             }
 
             isConstantAssertion = true;