Remove redundant IR generation of constants and unused IR main inlining

[ironcev]

Description

This PR:

• removes the redundant calls to compile_declarations function and the function itself. The function was used in early versions of Sway, but the way we compile items to IR has changed: functions are compiled at call site, and structs and enums are inlined at instantiation site. In the end, the function was only compiling constants, but that was already done in the dedicated compile_constants calls.
• removes the inline_main optimization which was aggressively inlining the whole program into main function. This was a necessity in early versions of Sway and is not used anymore.

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 44d5a37

Click to view benchmark

Test	Base	PR	%
code_action	5.4±0.02ms	5.4±0.04ms	0.00%
code_lens	290.9±9.71ns	293.4±9.39ns	+0.86%
compile	2.9±0.05s	2.9±0.03s	0.00%
completion	4.7±0.08ms	4.7±0.08ms	0.00%
did_change_with_caching	2.8±0.03s	2.8±0.03s	0.00%
document_symbol	936.1±34.81µs	1077.8±36.03µs	+15.14%
format	76.9±1.12ms	77.2±0.57ms	+0.39%
goto_definition	359.7±23.26µs	376.6±6.33µs	+4.70%
highlight	9.0±0.09ms	9.2±0.20ms	+2.22%
hover	468.3±18.26µs	483.4±4.95µs	+3.22%
idents_at_position	124.9±0.73µs	122.1±0.74µs	-2.24%
inlay_hints	649.8±12.18µs	678.5±38.63µs	+4.42%
on_enter	494.0±14.29ns	496.2±11.32ns	+0.45%
parent_decl_at_position	3.7±0.09ms	3.7±0.04ms	0.00%
prepare_rename	351.3±5.50µs	365.4±7.32µs	+4.01%
rename	9.6±0.12ms	9.6±0.18ms	0.00%
semantic_tokens	1016.0±8.32µs	1033.4±16.95µs	+1.71%
token_at_position	354.2±2.41µs	359.7±1.78µs	+1.55%
tokens_at_position	3.7±0.04ms	3.7±0.05ms	0.00%
tokens_for_file	421.7±1.54µs	419.8±2.48µs	-0.45%
traverse	41.7±0.93ms	42.1±1.00ms	+0.96%