Const Generics

[xunilrj]

This PR is the tracking-issue for the const_generics feature.
For more details go to: FuelLabs/sway-rfcs#42

• Feature toggle (Const generic feature toggle, parser and errors. #6926)
• Parsing (Const generic feature toggle, parser and errors. #6926)
• impl trait for arrays (impl trait for "const generics" #6946)
• impl trait for string arrays (Const generics for "string array" and len methods #7202)
  • AbiEncode/AbiDecode and other traits for string arrays (abiencode and abidecode for str array #7313)
  • Clone for string arrays (Clone implementation for string arrays #7290)
  • Hash for string arrays (Hash for string arrays #7293)
• structs (Support for const generics in structs #7076)
• enums (const-generics for enums #7163)
• standalone fns (const generics for standalone fns #7175)
• AbiEncode and AbiDecodefor arrays
  • Fix repeat array to allow [T; N] to be created (Implement array repeat without repeating item at the AST/CST trees #6901)
  • Allow [T; N] to be created unitialized
    • Cheap zero initialized arrays (Optimize initialization of array repeat when the initial value is zero #7299)
  • AbiEncode (impl trait for "const generics" #6946)
  • AbiDecode (AbiDecode for arrays using const_generics #7008)
• Eq, Hash and other core and std traits for arrays (impl PartialEq, Eq, Hash, Clone for array #7037)
  • Iterator for arrays (Iterator trait for arrays #7370)
  • Index trait (Index operator using Index trait #6356)
• Friendly error messages (Const generic feature toggle, parser and errors. #6926)
• Multiple "const generics" on the same enum/struct. (Better observability for the compiler #7250)
• Remove todo!()
• const_generics enabled by default