[clang] [clang][ExtractAPI] Fix assertion on invalid UTF-8 in doc comments (PR #212394)

[Prajwal Nadig via cfe-commits]

================
@@ -262,7 +262,11 @@ std::optional<Object> serializeDocComment(const DocComment &Comment) {
   Array LinesArray;
   for (const auto &CommentLine : Comment) {
     Object Line;
-    Line["text"] = CommentLine.Text;
+    // Source files are not required to be valid UTF-8. JSON values must be
----------------
snprajwal wrote:

This is a bit too broad of a statement

```suggestion
    // Comments in source files may contain invalid UTF-8. JSON values must be
```

https://github.com/llvm/llvm-project/pull/212394