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 `forwarding` directive should be optional for SIL instructions.
However, the current SIL parser put it as a requirement when there is a
comma follows after the main instruction components, which conflicts
with debug info directives like `loc` or `scope`. This patch teaches the
parser to treat `forwarding` as an optional directive.
Resolves SR-14814.
