[lldb][TypeSystemClang] Desugar an elaborated type before checking if it's a...

[lldb][TypeSystemClang] Desugar an elaborated type before checking if it's a typedef or getting a typedefed type

Summary:
Sometimes a result variable of some expression can be presented as an elaborated
type. In this case the methods `IsTypedefType()` and `GetTypedefedType()` of
`SBType` didn't work. This patch fixes that.

I didn't find the test for these API methods, so I added a basic test for this
too.

Reviewers: aprantl, teemperor, labath, leonid.mashinskiy

Reviewed By: teemperor

Subscribers: labath, lldb-commits

Tags: #lldb

Differential Revision: https://reviews.llvm.org/D78697