Adds occurrence auto completion

[AlexHolly]

more accurate auto completion for TextEdit contains informations about occurrences index for highlighting.

closes #21726

related #21181

please give it a good test @KoBeWi.

[KoBeWi]

Nice! Seems to work good in most cases, although I'd probably need to use it for some time and see how it feels overall.

Minor thing, but I found a case where it doesn't work as expected:

[AlexHolly]

Ah nice, I will try to fix this. Currently it orders only by word length maybe it can be optimized by order of occurrence index.

WIP
still not perfect

[AlexHolly]

Is there a way to remove the casts?
https://github.com/godotengine/godot/pull/21742/files#diff-0e0c9dec15a95e1c0d8e658a4ab39d4cR455

Is there a better way to pass a variable to the sort function?
https://github.com/godotengine/godot/pull/21742/files#diff-71709879dd36a28d4ff43c570b3b4c8bR5771
https://github.com/godotengine/godot/pull/21742/files#diff-0e0c9dec15a95e1c0d8e658a4ab39d4cR445
https://github.com/godotengine/godot/pull/21742/files#diff-0e0c9dec15a95e1c0d8e658a4ab39d4cR453

Some Examples

[akien-mga]

Moving to 3.2 milestone as we're about to enter the beta stage and release freeze for Godot 3.1. Only bug fixes against issues of the 3.1 milestone (or enhancements to core features of the 3.1 roadmap) will be considered until 3.1-stable is released.

Note: If it's merged after 3.1-stable is released, this change might be considered for cherry-picking into a later 3.1.x release.

[akien-mga]

This would be good to review and hopefully merge first, to reduce the complexity of the huge #21181 which includes it.

Given the timing I don't think it will cut it for 3.2 though, see also #21181 (comment) about changes to the TextEdit API for editor-specific needs.

[aaronfranke]

@AlexHolly Has there been any progress in solving the above issues?

I'm also wondering if the find_occurrences code could be simplified. Perhaps it could be a simple wrapper around find, each iteration starting the search from after the last one's end position.

[AlexHolly]

I will wait until this is resolved.

Maybe these changes should wait on the refactor described in #31739 so that it can be done with a better architecture. (#21181 (comment))

I like the split idea and will look into find_occurrences when it happens.

I think this should probably be split into separate PRs with a better separation of concerns, so that the code completion experience can be improved gradually with well tested iterations. (#21181 (comment))

[aaronfranke]

Closing this PR for now, it can be re-opened (or re-created) after #31739 is solved.