Support copying Math along with text

Currently, MathCAT's copy feature requires the user to navigate into the Math block. The first part of the request is to eliminate the need to navigate into the Math, press up arrow to get to the full expression, and then press Ctrl+c. It should be possible to copy Math via Ctrl+c even with just the review cursor on it without navigating into it. The second part of this request is to be able to copy neighbouring text in conjunction with Math blocks altogether using standard text selection commands followed by Ctrl+c. If I have a paragraph where the variabels are defined in text and the formula is in MathML, this would allow me to copy the entire line from the textbook in one shot and paste it in my study notes.

首先定位 MathCAT 現有的複製功能，以及 NVDA 外掛程式中的檢閱游標處理。在 Math 區塊上，以及在包含文字和 MathML 的段落上重現 Ctrl+c；當 Math 的直接複製，以及包含 Math 的相鄰文字的標準選取都能協同運作時，即表示完成。

由索引模型根據 Issue 內容生成。