Combine function bindings in projection dictionaries

[benl]

With this file

data Foo

project Foo where
  f True  = 4
  f False = 5

We get

benl@humboldt:~/devel/ddc/ddc-head-work$ bin/ddc -c test/Broken-skip/MergeProjFuns/Foo.ds 
./test/Broken-skip/MergeProjFuns/Foo.ddc.c:48: error: redefinition of ‘Foo_project_Foo_f’
./test/Broken-skip/MergeProjFuns/Foo.ddc.c:17: error: previous definition of ‘Foo_project_Foo_f’ was here
ddc: PANIC in Main.Invoke
        invokeSeaCompiler: compilation of C file failed.
            pathC = ./test/Broken-skip/MergeProjFuns/Foo.ddc.c

Desugarer needs to merge both equations for f.

Test is T55-MergeProjFuns