Eliminate the redundant instruction pair
```
%t = tuple (%0, %1, %2)
(%3, %4, %5) = destructure_tuple %t
```
and replace the results %3, %4, %5 with %0, %1, %2, respectively.
The same for structs.
A type (mostly classes) can be attributed with `@_semantics("arc.immortal")`.
ARC operations on values of such types are eliminated.
This is useful for the bridged SIL objects in the swift compiler sources.
The instance type of a metatype instruction is not necessarily a legal lowered SIL Type.
Lower the type before converting it to a SILType.
rdar://105502403
* begin_cow_mutation
* global_value
* strong_retain and strong_release
So far, those simplifications did only run in SILCombine. Now they are also considered in the swift Simplification pass.
