Add tab-complete coding suggestions when adding to `.executes` with `/configcommands build`

[willkroboth]

This suggestion is inspired by this example for Brigadier Suggestions from the CommandAPI.

Basically, there would be a command, functionline or something that gives suggestions for each step of writing a line of code when using /configcommands build. Some examples:

Typed: /functionline
Suggesting: [command, set, do, tag, if, goto, return]

Typed: /functionline set
Suggesting: All available variable names, ex: [<sender>, <commandIndex>]

Typed: /functionline set <commandIndex>
Suggesting: All the ways to make an Integer? ex: [Integer.new(, Integer.(, <commandIndex>]

Typed: /functionline command
Suggesting: All commands available on the server, use CommandAPI's CommandArgument

Once the user presses enter and the build menu intercepts the command as a message, if it is a /functionline command it can get intercepted and parsed to the correct syntax.

Sent: /functionLine set <commandIndex> Integer.("4")
Parsed: <commandIndex> = Integer.("4")

Sent: /functionLine command /say Hello World!
Parsed: /say Hello World!

This is probably easier said than done, and it's not very easy to say!