This PR "monomorphizes" the structure `Std.PRange shape α`, replacing it
with nine distinct structures `Std.Rcc`, `Std.Rco`, `Std.Rci` etc., one
for each possible shape of a range's bounds. This change was necessary
because the shape polymorphism is detrimental to attempts of automation.
**BREAKING CHANGE:** While range/slice notation itself is unchanged,
this essentially breaks the entire remaining (polymorphic) range and
slice API except for the dot-notation(`toList`, `iter`, ...). It is not
possible to deprecate old declarations that were formulated in a
shape-polymorphic way that is not available anymore.
This PR is the result of analyzing the elaborator performance regression
introduced by #10005. It makes the `workspaceSymboldNewRanges` and
`iterators` benchmarks less noisy. It also replaces some range-related
instances for `Nat` with shortcuts to the general-purpose instances.
This is a trade-off between the ergonomics and the synthesis cost of
having general-purpose instances.
