[llvm] [llvm][Docs] `_or_null` -> `_if_present` (PR #98586)

[David Spickett via llvm-commits]

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@@ -164,20 +164,20 @@ rarely have to include this file directly).
   efficient to use the ``InstVisitor`` class to dispatch over the instruction
   type directly.
 
-``isa_and_nonnull<>``:
-  The ``isa_and_nonnull<>`` operator works just like the ``isa<>`` operator,
+``isa_and_present<>``:
+  The ``isa_and_present<>`` operator works just like the ``isa<>`` operator,
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DavidSpickett wrote:

I see, isa_and_nonnull just calls isa_and_present.

https://github.com/llvm/llvm-project/pull/98586