Forc completions sub commands

[crodas]

Description

Fixes #5670

Add the ability to generate completions for subcommands

Subcommands may generate completions code optionally.

Checklist

• I have linked to any relevant issues.
• I have commented my code, particularly in hard-to-understand areas.
• I have updated the documentation where relevant (API docs, the reference, and the Sway book).
• I have added tests that prove my fix is effective or that my feature works.
• I have added (or requested a maintainer to add) the necessary Breaking* or New Feature labels where relevant.
• I have done my best to ensure that my PR adheres to the Fuel Labs Code Review Standards.
• I have requested a review from the relevant team or maintainers.

[github-actions]

Benchmark for 9bde546

Click to view benchmark

Test	Base	PR	%
code_action	5.1±0.11ms	5.4±0.08ms	+5.88%
code_lens	294.6±10.54ns	296.5±12.77ns	+0.64%
compile	3.0±0.03s	3.0±0.06s	0.00%
completion	4.6±0.06ms	4.8±0.05ms	+4.35%
did_change_with_caching	2.8±0.02s	2.8±0.02s	0.00%
document_symbol	988.0±15.72µs	967.1±34.22µs	-2.12%
format	73.3±1.34ms	70.8±1.34ms	-3.41%
goto_definition	362.4±7.06µs	376.8±6.28µs	+3.97%
highlight	8.8±0.13ms	9.2±0.21ms	+4.55%
hover	529.4±7.41µs	546.6±8.37µs	+3.25%
idents_at_position	123.6±0.55µs	122.0±0.40µs	-1.29%
inlay_hints	653.6±23.25µs	669.4±17.67µs	+2.42%
on_enter	483.3±5.91ns	482.9±15.83ns	-0.08%
parent_decl_at_position	3.6±0.01ms	3.7±0.02ms	+2.78%
prepare_rename	361.5±13.01µs	372.4±19.73µs	+3.02%
rename	9.1±0.13ms	9.5±0.13ms	+4.40%
semantic_tokens	1076.5±26.78µs	1061.0±24.06µs	-1.44%
token_at_position	362.0±2.33µs	363.3±2.71µs	+0.36%
tokens_at_position	3.6±0.04ms	3.7±0.03ms	+2.78%
tokens_for_file	413.2±2.17µs	415.5±2.20µs	+0.56%
traverse	37.3±0.91ms	37.5±1.10ms	+0.54%

[github-actions]

Benchmark for fbee83a

Click to view benchmark

Test	Base	PR	%
code_action	5.2±0.09ms	5.3±0.02ms	+1.92%
code_lens	290.6±7.77ns	291.1±9.52ns	+0.17%
compile	2.9±0.03s	3.0±0.02s	+3.45%
completion	4.8±0.20ms	4.9±0.07ms	+2.08%
did_change_with_caching	2.9±0.03s	2.9±0.03s	0.00%
document_symbol	972.3±8.51µs	952.3±26.75µs	-2.06%
format	73.8±1.36ms	70.3±1.17ms	-4.74%
goto_definition	374.1±7.24µs	368.8±4.21µs	-1.42%
highlight	8.8±0.19ms	9.1±0.02ms	+3.41%
hover	551.6±18.61µs	537.8±7.80µs	-2.50%
idents_at_position	123.5±0.65µs	122.0±0.39µs	-1.21%
inlay_hints	657.0±19.19µs	675.2±38.81µs	+2.77%
on_enter	483.9±13.08ns	476.4±12.56ns	-1.55%
parent_decl_at_position	3.6±0.06ms	3.7±0.02ms	+2.78%
prepare_rename	366.6±6.32µs	369.5±6.71µs	+0.79%
rename	9.2±0.02ms	9.5±0.12ms	+3.26%
semantic_tokens	1058.9±10.30µs	1060.3±30.38µs	+0.13%
token_at_position	366.3±2.26µs	361.3±3.48µs	-1.37%
tokens_at_position	3.6±0.04ms	3.7±0.02ms	+2.78%
tokens_for_file	413.5±4.28µs	417.3±1.63µs	+0.92%
traverse	38.5±1.44ms	37.8±0.86ms	-1.82%

[sdankel]

Why is this needed? Can you give some examples of subcommands that aren't working with the completions before?

We should have some unit tests for this. This could be useful: https://docs.rs/completest/0.0.12/completest/

[crodas]

Can you give some examples of subcommands that aren't working with the completions before?

None of the external subcommand (the plugins) were supported