Type annotations for instruction operands are omitted, e.g.
```
%3 = struct $S(%1, %2)
```
Operand types are redundant anyway and were only used for sanity checking in the SIL parser.
But: operand types _are_ printed if the definition of the operand value was not printed yet.
This happens:
* if the block with the definition appears after the block where the operand's instruction is located
* if a block or instruction is printed in isolation, e.g. in a debugger
The old behavior can be restored with `-Xllvm -sil-print-types`.
This option is added to many existing test files which check for operand types in their check-lines.
The new rule is that an argument will be exploded if one of the
following sets of conditions hold:
(1) (a) Specializing the function will result in a thunk. That is, the
thunk that is generated cannot be inlined everywhere.
(b) The argument has dead non-trivial leaves.
(c) The argument has fewer than three live leaves.
(2) (a) Specializing the function will not result in a thunk. That is,
the thunk that is generated will be inlined everywhere and
eliminated as dead code.
(b) The argument has dead potentially trivial leaves.
(c) The argument has fewer than six live leaves.
This change is based heavily on @gottesm's
https://github.com/apple/swift/pull/16756 .
rdar://problem/39957093
