* Disallow stores in the return -> argument path. When walking up in the EscapeUtils, it's allowed to follow stores. Therefore stores wouldn't be handled correctly.
* Also make sure that there is a return -> argument path at all
Fixes a wrong address-escaping effect in case the called function copies an indirect argument to a newly created object.
rdar://105133434
* split the `PassContext` into multiple protocols and structs: `Context`, `MutatingContext`, `FunctionPassContext` and `SimplifyContext`
* change how instruction passes work: implement the `simplify` function in conformance to `SILCombineSimplifyable`
* add a mechanism to add a callback for inserted instructions
This is consistent with `Type.isTrivial`.
Also, introduce corresponding properties in `Value`: `hasTrivialType` and `hasTrivialNonPointerType`, because
1. It's less to type than `Type.isTrivial(in: function)` because `Value` knows in which function it is.
2. It fixes the corner case where value is an `Undef`, which has not parent function.
