Use get_diagnostic_name

[camsteffen]

A new function tcx.get_diagnostic_name is available (after the next sync) and we should migrate existing code to use it in any case that multiple queries can be reduced to one.

For example (this is just one of a few different patterns that can be refactored):

// before
cx.tcx.is_diagnostic_item(sym::Vec, def_id)
    || cx.tcx.is_diagnostic_item(sym::HashMap, def_id)
    || cx.tcx.is_diagnostic_item(sym::HashSet, def_id)

// after
matches!(cx.tcx.get_diagnostic_name(def_id), Some(sym::Vec | sym::HashMap | sym::HashSet))

Also look for type_is_diagnotic_item calls which can be refactored using ty.ty_adt_def()?.did.