move documents from Session to ServerState

[JoshuaBatty]

Description

1st part of a code reorganization. Documents are now stored in ServerState meaning the documents can be shared across workspace members.

No new code was added.

related to #5856

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).
  • If my change requires substantial documentation changes, I have requested support from the DevRel team
• 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 85e919b

Click to view benchmark

Test	Base	PR	%
code_action	5.3±0.09ms	5.3±0.13ms	0.00%
code_lens	293.9±13.01ns	299.5±8.77ns	+1.91%
compile	6.0±0.05s	6.1±0.06s	+1.67%
completion	4.8±0.04ms	4.9±0.21ms	+2.08%
did_change_with_caching	6.0±0.06s	6.1±0.06s	+1.67%
document_symbol	946.5±14.08µs	962.4±41.17µs	+1.68%
format	76.3±1.23ms	76.1±1.96ms	-0.26%
goto_definition	366.9±9.05µs	365.1±5.42µs	-0.49%
highlight	8.8±0.06ms	8.7±0.03ms	-1.14%
hover	688.3±7.66µs	629.0±25.31µs	-8.62%
idents_at_position	123.6±0.59µs	122.7±0.89µs	-0.73%
inlay_hints	661.1±16.29µs	652.1±18.59µs	-1.36%
on_enter	480.7±13.78ns	488.5±18.24ns	+1.62%
parent_decl_at_position	3.6±0.03ms	3.6±0.03ms	0.00%
prepare_rename	371.8±7.20µs	362.3±4.26µs	-2.56%
rename	9.3±0.15ms	9.3±0.28ms	0.00%
semantic_tokens	1028.9±28.86µs	1024.7±10.77µs	-0.41%
token_at_position	366.7±3.05µs	364.6±3.05µs	-0.57%
tokens_at_position	3.6±0.02ms	3.6±0.17ms	0.00%
tokens_for_file	421.6±1.98µs	431.4±1.44µs	+2.32%
traverse	50.3±2.06ms	50.7±1.57ms	+0.80%

[sdankel]

LGTM

[github-actions]

Benchmark for 4d83c33

Click to view benchmark

Test	Base	PR	%
code_action	5.4±0.14ms	5.4±0.19ms	0.00%
code_lens	294.8±9.09ns	296.6±7.36ns	+0.61%
compile	6.3±0.12s	6.4±0.07s	+1.59%
completion	5.2±0.20ms	4.9±0.10ms	-5.77%
did_change_with_caching	6.3±0.14s	6.4±0.05s	+1.59%
document_symbol	1023.3±43.97µs	938.5±16.58µs	-8.29%
format	78.5±2.05ms	77.0±2.39ms	-1.91%
goto_definition	367.5±5.80µs	366.2±7.98µs	-0.35%
highlight	8.9±0.25ms	8.8±0.31ms	-1.12%
hover	609.0±18.45µs	610.5±21.39µs	+0.25%
idents_at_position	125.0±0.41µs	123.6±3.27µs	-1.12%
inlay_hints	664.7±37.59µs	657.4±31.27µs	-1.10%
on_enter	487.7±14.85ns	484.2±12.43ns	-0.72%
parent_decl_at_position	3.6±0.05ms	3.6±0.08ms	0.00%
prepare_rename	369.9±11.72µs	367.8±5.60µs	-0.57%
rename	9.8±0.23ms	9.7±0.28ms	-1.02%
semantic_tokens	1068.4±20.58µs	1052.8±42.79µs	-1.46%
token_at_position	367.5±5.94µs	364.1±2.91µs	-0.93%
tokens_at_position	3.7±0.10ms	3.6±0.09ms	-2.70%
tokens_for_file	416.9±4.45µs	433.6±8.15µs	+4.01%
traverse	50.7±2.16ms	50.9±2.11ms	+0.39%