Avoid adding new unneeded names to blocks in text roundtripping (#4943)

Previously the wat parser would turn this input:

(block
  (nop)
)

into something like this:

(block $block17
  (nop)
)

It just added a name all the time, in case the block is referred to by an index
later even though it doesn't have a name.

This PR makes us rountrip more precisely by not adding such names: if there
was no name before, and there is no break by index, then do not add a name.

In addition, this will be useful for non-nullable locals since whether a block has
a name or not matters there. Like #4912, this makes us more regular in our
usage of block names.

1 files changed, 7 insertions, 11 deletions

diff --git a/test/unreachable-code.wast.fromBinary b/test/unreachable-code.wast.fromBinary
index a93ffe730..67b8c30a6 100644
--- a/test/unreachable-code.wast.fromBinary
+++ b/test/unreachable-code.wast.fromBinary
@@ -44,22 +44,18 @@
  )
  (func $a-block-prepost
   (nop)
-  (block $label$1
-   (if
-    (i32.const 1)
-    (unreachable)
-   )
+  (if
+   (i32.const 1)
+   (unreachable)
   )
   (nop)
  )
  (func $b-block-prepost
   (nop)
-  (block $label$1
-   (if
-    (i32.const 1)
-    (unreachable)
-    (unreachable)
-   )
+  (if
+   (i32.const 1)
+   (unreachable)
+   (unreachable)
   )
  )
  (func $recurse