Fix RefineCallOpPattern in StablehloRefineShapes to preserve side-effecting callees

[christopherbate]

The constant-function replacement in RefineCallOpPattern did not check
whether the callee contains side-effecting operations. This caused calls
to functions with side effects (e.g. custom_call with
has_side_effect=true) to be silently erased. Guard the replacement with
a walk that checks for MemoryEffectOpInterface declarations.

[GleasonK]

nit - bool hasSideEffects = callee.walk(...).wasInterrupted(); to make it clear that interruption indicates side effect in the same line

[GleasonK]

Also I'm not sure if this is a complete solution. If there's a call op with a nested call op I don't think this catches its side effects. We had this problem in simplification as well and made a similar method:

stablehlo/stablehlo/transforms/optimization/StablehloAggressiveFolder.cpp

Lines 358 to 375 in a48c8e6

	bool hasAnyDeclaredSideEffects(Operation* op) {
	if (auto memInterface = dyn_cast<MemoryEffectOpInterface>(op)) {
	// Return true if the op explicitly declares any memory effects of its own.
	if (!memInterface.hasNoEffect()) return true;
	// The op has no direct memory effects. Return false if it has no recursive
	// memory effects, either.
	if (!op->hasTrait<OpTrait::HasRecursiveMemoryEffects>()) return false;
	}
	// The op doesn't declare any side effects of its own, but its regions could
	// still contain ops that do declare side effects. Recursively check them.
	for (Region& region : op->getRegions()) {
	for (Operation& nestedOp : region.getOps()) {
	if (hasAnyDeclaredSideEffects(&nestedOp)) return true;
	}
	}
	return false;
	}

A complete solution would likely require an analysis pass that maps call->side effects and does a full pass to calculate transitive side effects

[christopherbate]

Ok let me see if there's a way I can address this by computing it up front... I already didn't like the walk because the result should be cached