A name for a particular region used in emitting diagnostics. This name could be a generated
name like '1, a name used by the user like 'a, or a name like 'static.
Denotes the source of a region that is named by a RegionName. For example, a free region that
was named by the user would get NamedLateParamRegion and 'static lifetime would get
Static. This helps to print the right kinds of diagnostics.