Add a tweak for clangd to replace an auto keyword to the deduced type.
This way a user can declare something with auto and then have the IDE/clangd replace auto with whatever type clangd thinks it is. In case of long/complext types this makes is reduces writing effort for the user.
The functionality is similar to the hover over the auto keyword.
Example (from the header):
/// Before: /// auto x = Something(); /// ^^^^ /// After: /// MyClass x = Something(); /// ^^^^^^^
FYI, referring to a file opened as test:///foo.cpp as file:///clangd-test/file.cpp is wrong on Windows. I fixed this in rL374746.