Proposal: low-level-struct-improvements.md
Test plan: #59194

Parse and bind scoped modifier for parameters and locals; report binding error for scoped when compiling with -langversion:10 or earlier; emit modifier to metadata with LifetimeAnnotationAttribute. The scoped modifier can be applied to ref or to ref struct values.

The PR does not include:

• Changes to escape rules for scoped variables (see spec)
• conversions involving scoped
• scoped considered in overrides and interface implementation