Add support for Slices

[philberty]

We need to support slices to be able to compile the goal test case #682

see:

https://doc.rust-lang.org/book/ch04-03-slices.html
https://github.com/bminor/binutils-gdb/blob/79541a6d9220e800ebc5278594105982d6e1d80c/gdb/rust-lang.c#L157-L166
https://github.com/bminor/binutils-gdb/blob/79541a6d9220e800ebc5278594105982d6e1d80c/gdb/rust-lang.c#L299-L312

let a = [1, 2, 3, 4, 5];

let slice = &a[1..3];

• range lang items Add support for ranges and index lang items along with the TyTy::SliceType #974
• index lang items Add support for ranges and index lang items along with the TyTy::SliceType #974
• offset intrinsics Add more intrinsics and refactor how we implement them #1003
• Slice resolution and type code Add name resolution to slices #951
• ICE in canonical path generation of slices #1005 Add missing canonicalization of slices and raw pointer types #1007
• Add const_ptr lang item mappings #1008
• Add missing type resolution to slices and arrays #1009
• Add backend code-generation for the slice type and respect the layout of the FatPtr in libcore Add code generation for the slice type #1015
• hir lowering Add missing HIR lowering for SliceTypes #1016
• Bad unconstrained type parameter error #1019 Rewrite our unconstrained type-param error checking #1030
• Bad method resolution on pointers #1031 Fix bad copy-paste in can equal interface for pointer types #1033
• Bad placeholder type handling #1034
• unsized method resolution Add initial support for unsized method resolution #1045
• Bad inherent overlap error #1075
• Support mangling *const ptr and slices like *const [T] #1097
• Ensure unsize method resolutions actually unsize #1098
• Fix bad inherent overlap error #1099
• Slice support #1086