* JS initializers use original valueDecl, not mutated
target's valueDeclaration is set to the source's if it is not present.
This makes it incorrect to use getJSInitializerSymbol because it relies
on the symbol's valueDeclaration.
This fix just saves the original valueDeclaration before mutating and
uses that.
* Compare merged targetInitializer to target
Instead of the unmerged one
* Add test of stack overflow