add generic instantiations to generated docs

[andrewrk]

std lib example: file:///home/andy/dev/zig/build/zig-cache/docs/index.html#std;mem.copy (I recognize this is a file:/// URL; we don't have #3402 done yet)

The analysis dump actually has the entire list of std.mem.copy generic function instantiations, and they should be displayed here, along with doc comments.