Test that an (ill-typed) redeclaration of a name, which causes
types.Info.Defs to lack an entry, doesn't lead to gopls to crash in
renaming. Now, it proceeds with a partial rename.

See golang/go#70968

-- go.mod --
module example.com
go 1.18

-- a/a.go --
package a

type T int               //@ diag("T", re"T redeclared")
type T struct { f int }  //@ diag("T", re"T redeclared"), rename("f", "g", out)

-- @out/a/a.go --
@@ -4 +4 @@
-type T struct { f int }  //@ diag("T", re"T redeclared"), rename("f", "g", out)
+type T struct { g int }  //@ diag("T", re"T redeclared"), rename("f", "g", out)
