V719-009: Add test for find all references on multiple def names

Author: AdrienBoulanger

testsuite/ada_lsp/find_all_refs_defining_names/default.gpr

@@ -0,0 +1,3 @@
+project Default is
+end Default;
+

testsuite/ada_lsp/find_all_refs_defining_names/foo.adb

@@ -0,0 +1,7 @@
+procedure Foo is
+   X, Y : Integer := 1;
+begin
+   X := X + Y;
+   Y := X - Y;
+   X := X - Y;
+end Foo;