Rollup merge of #81665 - jacob-hughes:mir_doc_fix, r=estebank
Rollup merge of #81665 - jacob-hughes:mir_doc_fix, r=estebank

Fix out of date `Scalar` documentation

Scalars can represent integers up to `u128`, but the docs state otherwise.

aidancully/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust,graydon/rust,aidancully/rust,graydon/rust,aidancully/rust,aidancully/rust,graydon/rust,graydon/rust