Add a `tuple.drop` text pseudoinstruction (#6170)

We previously overloaded `drop` to mean both normal drops of single values and
also drops of tuple values. That works fine in the legacy text parser since it
can infer parent-child relationships directly from the s-expression structure of
the input, so it knows that a drop should drop an entire tuple if the
tuple-producing instruction is a child of the drop. The new text parser,
however, is much more like the binary parser in that it uses instruction types
to create parent-child instructions. The new parser always assumes that `drop`
is meant to drop just a single value because that's what it does in WebAssembly.

Since we want to continue to let `Drop` IR expressions consume tuples, and since
we will need a way to write tests for that IR pattern that work with the new
parser, introduce a new pseudoinstruction, `tuple.drop`, to represent drops of
tuples. This pseudoinstruction only exists in the text format and it parses to
normal `Drop` expressions. `tuple.drop` takes the arity of its operand as an
immediate, which will let the new parser parse it correctly in the future.

1 files changed, 1 insertions, 1 deletions

diff --git a/test/passes/precompute_all-features.wast b/test/passes/precompute_all-features.wast
index fad213a17..ca4aa1cbb 100644
--- a/test/passes/precompute_all-features.wast
+++ b/test/passes/precompute_all-features.wast
@@ -48,7 +48,7 @@
         (i32.const 1)
       )
     )
-    (drop
+    (tuple.drop 2
      (tuple.make 2
       (tuple.extract 0
        (tuple.make 2