[macOS] Add utf-8 character set meta tag for HTML clipboard content

This prevents unicode characters from becoming garbled when pasting the
clipboard content into an application that uses the HTML content
instead of the text data.

This mirrors the behavior of Chromium's clipboard adaptation for macOS

Fixes: QTBUG-75391
Change-Id: I033819a2caf3410509e90c9bc38c9830d184149d
Reviewed-by: Jüri Valdmann <[email protected]>
(cherry picked from commit 7b5cb51)

Author: mibrunin

src/core/clipboard_qt.cpp

@@ -235,7 +235,14 @@ void ClipboardQt::WriteText(const char* text_data, size_t text_len)
 
 void ClipboardQt::WriteHTML(const char* markup_data, size_t markup_len, const char* url_data, size_t url_len)
 {
-    getUncommittedData()->setHtml(QString::fromUtf8(markup_data, markup_len));
+    QString markup_string = QString::fromUtf8(markup_data, markup_len);
+#if defined (Q_OS_MACOS)
+    // We need to prepend the charset on macOS to prevent garbled Unicode characters
+    // when pasting to certain applications (e.g. Notes, TextEdit)
+    // Mirrors the behavior in ui/base/clipboard/clipboard_mac.mm in Chromium.
+    markup_string.prepend(QLatin1String("<meta charset='utf-8'>"));
+#endif
+    getUncommittedData()->setHtml(markup_string);
 }
 
 void ClipboardQt::WriteRTF(const char* rtf_data, size_t data_len)