[DebugInfo] Add debug info to the values emitted in GlobalStructInference

[kripken]

Previously the replacement select got the debug info, but we should also copy it
to the values, as often optimizations lead to one of those values remaining by
itself.

Similar to #6652 in general form.

Diff without whitespace is much shorter.

See the very last commit to see the impact on the new test.

[aheejin]

Suggested change

	auto* get = builder.makeGlobalGet(value.globals[0],
	ret = builder.makeGlobalGet(value.globals[0],

Nit: Can we do this and remove ret = get below?

[kripken]

That almost works, but we need the type to be more specific than Expression* on line 441, where we use get in a place that must be GlobalGet*.

[aheejin]

Why did the select have debug info even before this PR (and not the children)?

[kripken]

The select received it because replaceCurrent copies debug info, and we replace the struct.get with the select. But it doesn't copy recursively into children (we've considered that before, but it's not clear if it's correct, and would be slower).

[aheejin]

I thought we were doing that..?

binaryen/src/wasm-traversal.h

Lines 125 to 129 in cdf8139

	// Copy debug info, if present.
	if (currFunction) {
	debuginfo::copyOriginalToReplacement(
	getCurrent(), expression, currFunction);
	}

[kripken]

Yes, but not recursively, just on the replacement:

binaryen/src/ir/debuginfo.h

Line 43 in cdf8139

debugLocations[replacement] = iter->second;

So the select gets it, but not the select's children.