Require `then` and `else` with `if` (#6201)

We previously supported (and primarily used) a non-standard text format for
conditionals in which the condition, if-true expression, and if-false expression
were all simply s-expression children of the `if` expression. The standard text
format, however, requires the use of `then` and `else` forms to introduce the
if-true and if-false arms of the conditional. Update the legacy text parser to
require the standard format and update all tests to match. Update the printer to
print the standard format as well.

The .wast and .wat test inputs were mechanically updated with this script:
https://gist.github.com/tlively/85ae7f01f92f772241ec994c840ccbb1

1 files changed, 26 insertions, 10 deletions

diff --git a/test/passes/remove-unused-brs_shrink-level=1_ignore-implicit-traps.wast b/test/passes/remove-unused-brs_shrink-level=1_ignore-implicit-traps.wast
index 08d3fb318..4f15dc9c0 100644
--- a/test/passes/remove-unused-brs_shrink-level=1_ignore-implicit-traps.wast
+++ b/test/passes/remove-unused-brs_shrink-level=1_ignore-implicit-traps.wast
@@ -7,33 +7,49 @@
     (drop
       (if (result i32) ;; with shrinking, this can become a select
         (i32.const 1)
-        (block $block1 (result i32)
-          (i32.const 12)
+        (then
+          (block $block1 (result i32)
+            (i32.const 12)
+          )
         )
-        (block $block3 (result i32)
-          (i32.const 27)
+        (else
+          (block $block3 (result i32)
+            (i32.const 27)
+          )
         )
       )
     )
     (drop
       (if (result i32)
         (i32.const 1)
-        (i32.load (i32.const 10)) ;; load may have side effects, unless ignored
-        (i32.const 27)
+        (then
+          (i32.load (i32.const 10)) ;; load may have side effects, unless ignored
+        )
+        (else
+          (i32.const 27)
+        )
       )
     )
     (drop
       (if (result i32)
         (i32.const 1)
-        (i32.rem_s (i32.const 11) (i32.const 12)) ;; rem may have side effects, unless ignored
-        (i32.const 27)
+        (then
+          (i32.rem_s (i32.const 11) (i32.const 12)) ;; rem may have side effects, unless ignored
+        )
+        (else
+          (i32.const 27)
+        )
       )
     )
     (drop
       (if (result i32)
         (i32.const 1)
-        (i32.trunc_f64_u (f64.const 12.34)) ;; float to int may have side effects, unless ignored
-        (i32.const 27)
+        (then
+          (i32.trunc_f64_u (f64.const 12.34)) ;; float to int may have side effects, unless ignored
+        )
+        (else
+          (i32.const 27)
+        )
       )
     )
     (i32.const 0)