Convert to PROGMEM

[drashna]

This converts the array to PROGMEM, in theory, and should reduce system memory usage on AVR boards. ARM doesn't use progmem, but has a lot more memory, so shouldn't be an issue

[getreuer]

Thank you @drashna ! This is great. I verified that this works on Dactyl Ergodox.

I was at first concerned about the overhead of reading from PROGMEM, since the code reads some number of bytes from PROGMEM on every key press, and in a (cache unfriendly) jumping pattern to follow trie branches. So I did some benchmarking to check. Method: on every alpha key press event, I used QMK's timer_read32() and timer_elapsed32() around the process_autocorrection() call. Since this has only millisecond resolution, I accumulate the elapsed time across multiple key events to get a sub-millisecond estimate the average. For normal typing, estimated over a few thousand keystrokes on Monkeytype exercises, I get:

Version	Average time
Without PROGMEM	26 μs
With PROGMEM	20 μs

That's comparable if not better!

In order to merge this, I need you to sign a Contributor License Agreement (CLA) at https://cla.developers.google.com/. You (or your employer) retain the copyright to your contribution. This simply gives permission to use and redistribute your contributions as part of the project. See https://cla.developers.google.com/ for your current agreements on file or to sign a new one.

[drashna]

I'm glad to hear that it seems to be even faster! Though, my primary concern was for memory usage on AVR, which can be very limited. For ARM, it doesn't use progmem, at all, but I'm used to keeping both in mind.

And the CLA "signed".