Add string slices to supported types message in match expressions

[ironcev]

Description

This PR adds string slices to CURRENTLY_SUPPORTED_TYPES_MESSAGE in match expressions. The support for string slices is added in #6202.

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 c0353e1

Click to view benchmark

Test	Base	PR	%
code_action	5.1±0.41ms	5.2±0.07ms	+1.96%
code_lens	298.5±9.50ns	287.1±8.95ns	-3.82%
compile	2.5±0.03s	2.5±0.04s	0.00%
completion	4.5±0.06ms	4.7±0.05ms	+4.44%
did_change_with_caching	2.5±0.02s	2.5±0.03s	0.00%
document_symbol	909.7±34.12µs	924.3±22.17µs	+1.60%
format	70.7±0.95ms	71.3±0.84ms	+0.85%
goto_definition	334.7±4.89µs	346.6±7.16µs	+3.56%
highlight	8.7±0.03ms	9.0±0.08ms	+3.45%
hover	496.5±6.36µs	501.0±6.59µs	+0.91%
idents_at_position	118.2±0.46µs	117.8±0.49µs	-0.34%
inlay_hints	631.8±15.12µs	640.5±19.38µs	+1.38%
on_enter	450.7±17.39ns	455.9±12.85ns	+1.15%
parent_decl_at_position	3.6±0.05ms	3.7±0.04ms	+2.78%
prepare_rename	336.9±6.12µs	342.9±7.50µs	+1.78%
rename	8.9±0.24ms	9.3±0.03ms	+4.49%
semantic_tokens	1263.7±14.34µs	1275.2±8.00µs	+0.91%
token_at_position	340.7±3.20µs	335.3±2.99µs	-1.58%
tokens_at_position	3.6±0.07ms	3.7±0.02ms	+2.78%
tokens_for_file	403.8±9.61µs	398.8±3.18µs	-1.24%
traverse	36.9±1.06ms	37.2±1.14ms	+0.81%