[lldb][TypeSystemClang] Unconditionally set access control to AS_public (#182956)
This patch removes all our manual adjustments to the access control
specifiers of Clang decls we create from DWARF.
This has led to occasional subtle bugs in the past (the latest being
https://github.com/llvm/llvm-project/issues/171913) and it's ultimately
redundant because Clang already has provisions for LLDB to bypass access
control for C++ and Objective-C. Access control doesn't affect name
lookup so really we're doing a lot of bookkeeping for not much benefit.
The only "feature" that relied on this was that `type lookup <foo>`
would print the access specifier in the output structure layout. I'm not
convinced that's worth keeping the infrastructure in place for (but
happy to be convinced otherwise).
I'd rather lean fully into the Clang access control bypass instead.
Note, i still kept the `AccessType` parameters to the various
`TypeSystemClang` APIs to reduce the size of the diff. A follow-up NFC
change will remove those parameters and adjust all the call-sites.