[Feature] Add optional text preview/spell check to on screen keyboard

[brendenhoffman]

With such a small screen, you often have to choose between obscuring something like your game to watch your text input, or cover the text input to watch your game. Due to the difficulty of typing on the Deck, it's easy to make spelling mistakes, one needs to see what they are typing, but they shouldn't have to cover what they are doing to do so. This is rarely a problem on your mobile phone, even if you have to type without seeing your text because they almost always incorporate some sort of text preview in the form of spell check.

In the case of spell check, it would indeed be useful, but I think for the deck specifically, it would need some special considerations:

• it must always show current typed word, delimited by spaces
• the dictionary could be rudimentary for spelling mistakes. There is a lot of use of words that aren't real in gaming that shouldn't be corrected
• the dictionary would benefit from automatically adding frequently used words to the dictionary
• the dictionary should know to correct missing letters and double tapped letters, this should be prioritized over accidentally hitting bordering keys and derelict letters due to the deck having ample sized keys, but more difficult key presses.

Current SteamOS version 3.3 beta