[DWARFLinker] Don't duplicate classes with in-class static decls (#196442)
An in-class static declaration was forced to PlainDwarf placement and
cascaded that up to its enclosing class. If the class was already in the
type table via the out-of-line definition's specification, it ended up
with Both placement and cloneDIE emitted two copies. Keep in-class
static declarations in the type table so they stay with their enclosing
type.