refactor: rename completion functions

[akinomyoga]

This is a suggestion for the naming of completion functions (i.e., the functions that are supposed to be specified to complete -F) defined in bash_completion: In this PR, the completion functions in bash_completion have the names of the form _comp_complete_*.

[scop]

Not sure about this one; it's certainly clearer this way, but if we go with this, it kind of asks renaming of _comp_cmd_* similarly as well -- they're intended for compgen -F, too. But that would then take them further from their _comp_cmd_*__* utilities, and those should not be renamed according to this plan.

[akinomyoga]

Hmm, that is a good point. Do you have any other ideas? The completion functions (which call _comp_initialize, etc. at the top) clearly form a class of the functions, but that classification is not so clear from the function names in the current form. I think that having a particular form of names for this function class makes it easier to find and choose the correct function.

For consistency, the current way is already not so consistent; while the completion function for a specific command is named as _comp_cmd_${CmdName}, there doesn't seem any naming rules for the general completion functions defined in the main file bash_completion. Besides, looking at the section of Naming in api-and-naming.md, I think there is already a separation of the naming rule between the functions in bash_completion and those in completions/*. Possible solutions would be

1. To adopt this PR. As pointed out, this seems to introduce some inconsistency in the naming rule of the completion functions in the main file and specific completion functions.
2. One way is to give up giving them a particular function name and to keep the completion functions in bash_completion at the top level directly under _comp_*.
3. The other way around might be to rename all the other functions (which are not completion functions) to _comp_util_* (probably except for _comp_compgen_*). I've checked the list of functions in bash_completion, but it doesn't seem right to rename everything including _comp_initialize to _comp_util_initialize, _comp_load to _comp_util_load.
4. Or to rename specific-command completion functions as _comp_cmd_${CmdName}_complete or _comp_cmd_${CmdName}_cmoplete_${CmdName}. This seems redundant.
5. (Others?)

Currently, I feel options 1 and 2 would be realistic. Considering the fact that we already have a separation in the naming rule of functions in the main file bash_completion and specific completions completions/*, option 1 appears acceptable to me.

In any case, I should probably update doc/api-and-naming.md as well.

[scop]

After this, _comp_complete_load is in an incorrect namespace as it does something else, we should look into renaming it to something else.

[akinomyoga]

In my thinking, _comp_complete_load is still in the same class of "completion functions" in the sense that _comp_complete_load is intended to be specified to complete -F.

Actually, when I introduced the name _comp_complete_load in d9082d2 (#1032), I already anticipated the changes of this PR and made consistent with this PR. This is also one of the reasons that I split _completion_loader into two functions with different purposes, _comp_load (for a utility to purely load a completion) and _comp_complete_load (for complete -F) (as in comment d9082d2#r1295226734).

[scop]

Ah, indeed. No problem then, merging. Thanks!

[akinomyoga]

squashed typo fix complet{or => er}

[scop]

For some reason GH is stalling in "Checking for ability to merge automatically…" for me, feel free to merge at your convenience if it works for you.

[akinomyoga]

Thank you!