[llvm] [Dexter] Update Dexter lit substitutions, making lldb-dap the default (PR #155838)

[Stephen Tozer via llvm-commits]

SLTozer wrote:

Planning on ignoring the code formatting errors for this one, as it's just reporting on test files, and the suggested fixes would break the tests.

https://github.com/llvm/llvm-project/pull/155838