Make filter APIs for UseList chainable by adding them to Sequence where Element == Operand
For example, it allows to write:
```
let singleUse = value.uses.ignoreDebugUses.ignoreUsers(ofType: EndAccessInst.self).singleUse
```
Also, add `UseList.getSingleUser(notOfType:)`
* add `UnownedRetainInst` and `UnownedReleaseInst`
* add `var value` to `RetainValueInst` and `ReleaseValueInst`
* make the protocol `UnaryInstruction` be an `Instruction`
* add `var Type.isValueTypeWithDeinit`
* add `var Type.isUnownedStorageType`
* add `var OperandArray.values`
Let's lldb's `po` command not print any "internal" properties of the conforming type.
This is useful if the `description` already contains all the information of a type instance.
Improve block/instruction lists and similar collections
* pretty print collections in the form “[a, b, c]”
* also do this for lazy sequences
* define a custom Mirror
* in a collection, only print the name of blocks, functions and globals (instead of the full object)
* replace `BasicBlock.reverseInstructions` with `BasicBlock.instructions.reversed()` - in an efficient way
