[Strings] Represent string values as WTF-16 internally (#6418)

WTF-16, i.e. arbitrary sequences of 16-bit values, is the encoding of Java and
JavaScript strings, and using the same encoding makes the interpretation of
string operations trivial, even when accounting for non-ascii characters.
Specifically, use little-endian WTF-16.

Re-encode string constants from WTF-8 to WTF-16 in the parsers, then back to
WTF-8 in the writers. Update the constructor for string `Literal`s to interpret
the string as WTF-16 and store a sequence of WTF-16 code units, i.e. 16-bit
integers. Update `Builder::makeConstantExpression` accordingly to convert from
the new `Literal` string representation back to a WTF-16 string.

Update the interpreter to remove the logic for detecting non-ascii characters
and bailing out. The naive implementations of all the string operations are
correct now that our string encoding matches the JS string encoding.

1 files changed, 1 insertions, 1 deletions

diff --git a/src/literal.h b/src/literal.h
index 971cc8b3e..a4017f6ec 100644
--- a/src/literal.h
+++ b/src/literal.h
@@ -85,7 +85,7 @@ public:
     assert(type.isSignature());
   }
   explicit Literal(std::shared_ptr<GCData> gcData, HeapType type);
-  explicit Literal(std::string string);
+  explicit Literal(std::string_view string);
   Literal(const Literal& other);
   Literal& operator=(const Literal& other);
   ~Literal();