Issue 4125 - [emscripten] Convert filter classes to C++

compiled/String.h

 #pragma once
 
 #include <cstddef>
 #include <cstring>
 #include <algorithm>
 
 #include <emscripten.h>
 
 #include "debug.h"
 
@@ skipping 170 matching lines @@
   explicit DependentString(value_type* buf, size_type len)
       : String(buf, len, READ_WRITE)
   {
   }
 
   explicit DependentString(const value_type* buf, size_type len)
       : String(const_cast<value_type*>(buf), len, READ_ONLY)
   {
   }
 
-  DependentString(String& str, size_type pos = 0, size_type len = npos)
+  explicit DependentString(String& str, size_type pos = 0, size_type len = npos)
       : String(
           str.mBuf + std::min(pos, str.length()),
           std::min(len, str.length() - std::min(pos, str.length())),
           str.is_readOnly() ? READ_ONLY : READ_WRITE
         )
   {
   }
 
-  DependentString(const String& str, size_type pos = 0,
+  explicit DependentString(const String& str, size_type pos = 0,
       size_type len = npos)
       : String(
           str.mBuf + std::min(pos, str.length()),
           std::min(len, str.length() - std::min(pos, str.length())),
           READ_ONLY
         )
   {
   }
 
   void reset(value_type* buf, size_type len)
@@ skipping 32 matching lines @@
 inline void String_assert_readonly(bool readOnly)
 {
   assert(!readOnly, u"Writing access to a read-only string"_str);
 }
 
 class OwnedString : public String
 {
 private:
   void grow(size_type additionalSize)
   {
-    auto newValue = OwnedString(length() + additionalSize);
+    OwnedString newValue(length() + additionalSize);
     if (length() > 0)
       std::memcpy(newValue.mBuf, mBuf, sizeof(value_type) * length());
     *this = std::move(newValue);
   }
 
 public:
   explicit OwnedString(size_type len = 0)
       : String(nullptr, len, READ_WRITE)
   {
     if (len)
@@ skipping 70 matching lines @@
   void append(const String& str)
   {
     append(str.mBuf, str.length());
   }
 
   void append(value_type c)
   {
     append(&c, 1);
   }
 };