T2S - uppercase shortcuts are not spelled out

[ivan-homoliak-sutd]

I tested English pronunciation and observed that the uppercase shortcuts are not spelled out, e.g., GPT, GPU.

[nikito]

Related to #125
This is more or less the same limitation of SpeechT5, and TTS in general. TTS doesn't always do well with acroynms because it is trying to parse out the phonemes of the text as if it were words. Of course, GPU/GPT are not words, but TTS on its own isn't smart enough to know that, so pre-processing is needed to split these out, such as 'G P U' or 'G P T'. As mentioned in #125 this is something we will look into more as willow advances. :)