better `typeDefiniton` on functions

[xdBronch]

currently asking for the type definition of a function just goes to the beginning of the functions definition. im not sure what exactly is the general consensus for what this should do (or is it specified exactly in the standard?) but clangd and rust-analyzer seem to take you to the definition of the return type, dont have anything else installed rn :p. naively i think maybe itd be nice to give you the definitions of all the params too?