Phonetic Mode: Option to phonetically spell 1-letter words in Math blocks

Mathematicians seem to enjoy notation overload. In particular, I encounter many Math problems where letters that sound far too similar are used together. I find myself needing to navigate Math blocks frequently just to tell the m's and n's apart, or the b's and d's, or the s's and f's. But even once in, commands like NVDA+. (laptop layout) to read the current character don't work. That bug may merit a ticket of its own. For this one though, I share that as motivation for a phonetic mode feature request. When enabled, MathCAT would read the phonetic corresponding to a letter instead of the letter itself for all 1-letter words in Math blocks. This would contribute considerable verbosity so it should be turned off by default. However, I think enable phonetic mode, read current line, and then disable phonetic mode would be a much better workflow than trying to navigate the Math block and arrowing around to try to hear the confusing letter in isolation a couple times.

首先定位 MathCAT 對 Math 區塊內單字母單詞的處理方式，以及現有的設定或閱讀模式進入點。確認 NVDA 如何呼叫 MathCAT，然後將完成條件定義為：提供一個可選擇啟用的音標模式，為所有單字母 Math 單詞讀取音標；該模式預設關閉，並且可以為一次行讀取啟用後再關閉。

由索引模型根據 Issue 內容生成。