[lldb][DataFormatter] Unwrap reference type when formatting std::unordered_map (#145872)
Desugar any potential references/typedefs before checking
`isStdTemplate`. Previously, the typename might've been:
```
const std::unordered_map<...> &
```
for references. This patch gets the pointee type before grabbing the
canonical type. `GetNonReferenceType` will unwrap typedefs too, so we
should always end up with a non-reference before we get to
`GetCanonicalType`.
https://github.com/llvm/llvm-project/issues/145847