[Parser] Parse wast scripts (#6581)

The spec tests use an extension of the standard text format that includes
various commands and assertions used to test WebAssembly implementations. Add a
utility to parse this extended WebAssembly script format and use it in
wasm-shell to check that it parses our spec tests without error. Fix a few
errors the new parser found in our spec tests.

A future PR will rewrite wasm-shell to interpret the results of the new parser,
but for now to keep the diff smaller, do not do anything with the new parser
except check for errors.

Author: tlively

src/parser/CMakeLists.txt

@@ -3,6 +3,7 @@ set(parser_SOURCES
  context-decls.cpp
  context-defs.cpp
  lexer.cpp
+ wast-parser.cpp
  wat-parser.cpp
  ${parser_HEADERS}
 )

src/parser/contexts.h

@@ -1696,7 +1696,7 @@ struct ParseDefsCtx : TypeParserCtx<ParseDefsCtx> {
     return Builder::addVar(func, name, type);
   }
 
-  Result<Expression*> makeExpr() { return irBuilder.build(); }
+  Result<Expression*> makeExpr() { return withLoc(irBuilder.build()); }
 
   Memarg getMemarg(uint64_t offset, uint32_t align) { return {offset, align}; }