tests: add more merge_import tests for rust-lang#3808

Author: calebcartwright

tests/source/merge_imports.rs

@@ -29,3 +29,6 @@ use e::{self as foo};
 use f::{self, b};
 use g::a;
 use g::{self, b};
+use h::{a};
+use i::a::{self};
+use j::{a::{self}};

tests/target/merge_imports.rs

@@ -20,3 +20,6 @@ use d::{self};
 use e::{self as foo};
 use f::{self, b};
 use g::{self, a, b};
+use h::a;
+use i::a::{self};
+use j::a::{self};