[clang] [lldb] [clang] remove IsDefaulted bit from TemplateArgument (PR #155120)

[Matheus Izvekov via cfe-commits]

mizvekov wrote:

> If the change breaks LLDB then you should also fix that break as well.

Yes of course, but the parts already in the PR can be reviewed independently of that.

https://github.com/llvm/llvm-project/pull/155120