DX request: add hook to allow programmatic alteration of returned matches

It looks like it's currently impossible to make alterations to the json returned by views_autocomplete_filter(). I'm thinking it would really be useful to offer a hook here so other modules can make alterations.

I realized that the results returned are generated by views, which is hugely customizable, flexible and an all-around fantastic tool, but there are potential use cases where results acquired from views may need other alterations within the context of this module. For example:

• Programmatic customization of empty results messages (too few characters or no results returned). Those messages can be statically changed with a string override, but not programmatically. See also: #2093553: Customize empty result message programmatically .
• Removal of empty results behavior for custom applications where this does not make sense.
• Allowing the ability for selective theming of individual match results. A theme function may also be useful for the individual match results, but that's probably another topic entirely, for now I'm just interested in opening the door for alterations.
• Allowing the addition of match results, or headers/titles for groups or match results. See also #2285637: Show title above result list.
• Very specialized cases where match results need to be customized beyond the views result set.

I know this would add an extra function call to each lookup, but something like a drupal_alter() should be a totally negligible addition as far as performance is concerned.