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

2 files changed, 23 insertions, 17 deletions

diff --git a/test/gtest/cfg.cpp b/test/gtest/cfg.cpp
index bf3742bc1..c78eb218a 100644
--- a/test/gtest/cfg.cpp
+++ b/test/gtest/cfg.cpp
@@ -26,7 +26,7 @@ TEST_F(CFGTest, Print) {
         (drop
           (if (result i32)
             (i32.const 1)
-            (block
+            (then
               (loop $loop
                 (br_if $loop
                   (i32.const 2)
@@ -34,8 +34,10 @@ TEST_F(CFGTest, Print) {
               )
               (i32.const 3)
             )
-            (return
-              (i32.const 4)
+            (else
+              (return
+               (i32.const 4)
+              )
             )
           )
         )
@@ -65,7 +67,7 @@ TEST_F(CFGTest, Print) {
 ;; preds: [3], succs: [6]
 4:
   6: i32.const 3
-  7: block
+  7: block (result i32)
 
 ;; preds: [0], succs: [7]
 5:
@@ -230,7 +232,7 @@ TEST_F(CFGTest, BlockIndexes) {
       (func $foo
         (if
           (i32.const 1)
-          (block
+          (then
             (drop
               (i32.const 2)
             )
@@ -343,11 +345,15 @@ TEST_F(CFGTest, ReachingDefinitionsIf) {
             (local.get $a)
             (i32.const 2)
           )
-          (local.set $b
-            (i32.const 3)
+          (then
+            (local.set $b
+              (i32.const 3)
+            )
           )
-          (local.set $a
-            (i32.const 4)
+          (else
+            (local.set $a
+              (i32.const 4)
+            )
           )
         )
         (drop
diff --git a/test/gtest/stringify.cpp b/test/gtest/stringify.cpp
index 3e50c6d4c..c38c29d80 100644
--- a/test/gtest/stringify.cpp
+++ b/test/gtest/stringify.cpp
@@ -20,13 +20,13 @@ TEST_F(StringifyTest, Print) {
       )
       (block $block_b
         (drop (if (i32.const 0)
-          (i32.const 40)
-          (i32.const 5)
+          (then (i32.const 40))
+          (else (i32.const 5))
         ))
       )
       (block $block_c
         (drop (if (i32.const 1)
-          (i32.const 30)
+          (then (i32.const 30))
         ))
       )
       (block $block_d
@@ -150,13 +150,13 @@ static auto dupModuleText = R"wasm(
         )
         (block $block_b
           (drop (if (i32.const 0)
-            (i32.const 40)
-            (i32.const 5)
+            (then (i32.const 40))
+            (else (i32.const 5))
           ))
         )
         (block $block_c
           (drop (if (i32.const 1)
-            (i32.const 30)
+            (then (i32.const 30))
           ))
         )
         (block $block_d
@@ -165,12 +165,12 @@ static auto dupModuleText = R"wasm(
         )
         (block $block_e
           (drop (if (i32.const 1)
-            (i32.const 30)
+            (then (i32.const 30))
           ))
         )
         (block $block_f
           (drop (if (i32.const 0)
-            (i32.const 30)
+            (then (i32.const 30))
           ))
         )
       )