Split declarations and definitions to improve compile times when editing (#13332)

* Split FileStream declarations and definitions

* Split JobPool declarations and definitions

* Split StringBuilder declarations and definitions

* Split StringReader declarations and definitions

* Split ZoomLevel declarations and definitions

* Fix missing include in FileClassifier.cpp

* Remove pragma once from source files

* Fix missing include in StringBuilder.h

* Update Xcode project

* Fix compilation of tests

Co-authored-by: Michael Steenbeek <m.o.steenbeek@gmail.com>

src/openrct2/core/StringBuilder.cpp

@@ -0,0 +1,72 @@
+/*****************************************************************************
+ * Copyright (c) 2014-2020 OpenRCT2 developers
+ *
+ * For a complete list of all authors, please refer to contributors.md
+ * Interested in contributing? Visit https://github.com/OpenRCT2/OpenRCT2
+ *
+ * OpenRCT2 is licensed under the GNU General Public License version 3.
+ *****************************************************************************/
+
+#include "StringBuilder.h"
+
+#include "String.hpp"
+
+#include <algorithm>
+#include <iterator>
+
+StringBuilder::StringBuilder(size_t capacity)
+{
+    _buffer.reserve(capacity);
+}
+
+void StringBuilder::Append(int32_t codepoint)
+{
+    Append(static_cast<codepoint_t>(codepoint));
+}
+
+void StringBuilder::Append(codepoint_t codepoint)
+{
+    size_t codepointLength = String::GetCodepointLength(codepoint);
+    std::basic_string<utf8> data(codepointLength, {});
+    String::WriteCodepoint(data.data(), codepoint);
+    _buffer.insert(_buffer.end(), data.begin(), data.end());
+}
+
+void StringBuilder::Append(const utf8* text)
+{
+    size_t textLength = String::SizeOf(text);
+    Append(text, textLength);
+}
+
+void StringBuilder::Append(const utf8* text, size_t textLength)
+{
+    _buffer.insert(_buffer.end(), text, text + textLength);
+}
+
+void StringBuilder::Append(const StringBuilder* sb)
+{
+    Append(sb->GetBuffer(), sb->GetLength());
+}
+
+void StringBuilder::Clear()
+{
+    _buffer.clear();
+}
+
+std::string StringBuilder::GetStdString() const
+{
+    return std::string(GetBuffer(), GetLength());
+}
+
+const utf8* StringBuilder::GetBuffer() const
+{
+    // buffer may be empty, so return an immutable empty string
+    if (_buffer.empty())
+        return "";
+    return _buffer.c_str();
+}
+
+size_t StringBuilder::GetLength() const
+{
+    return _buffer.size();
+}