`dbDelta()` compares the index definitions against the result of `SHOW INDEX FROM $table_name`. This requires a specific format so indices are not unnecessarily re-created. This format wasn't ensured, until now.
* Parse the raw index definition to extract the type, name and columns so a normalized definition can be built (#20263, #34873).
* Standardize on uppercase types (#34871) and on 'KEY'. 'INDEX' is only a synonym for 'KEY'.
* Escape index names with backticks (#20263).
* Normalize columns: Ignore ASC and DESC definitions (#34959), remove whitespaces (#34869) and escape column names with backticks (#20263).
* Add backticks to all index change queries (#20263).
Props ocean90, pento, kurtpayne.
Fixes#20263, #34869, #34871, #34873, #34959.
git-svn-id: https://develop.svn.wordpress.org/trunk@37583 602fd350-edb4-49c9-b593-d223f7449a82
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