[gdb/ada] Move identical enums handling later

[gdb/ada] Move identical enums handling later

When running test-case gdb.ada/arr_acc_idx_w_gap.exp with target board
cc-with-dwz, I run into:
...
(gdb) print enum_with_gaps'enum_rep(lit3)^M
'Enum_Rep requires argument to have same type as enum^M
(gdb) FAIL: gdb.ada/arr_acc_idx_w_gap.exp: enum_rep
...

With target_board unix, we have instead:
...
(gdb) print enum_with_gaps'enum_rep(lit3)^M
$16 = 13^M
(gdb) PASS: gdb.ada/arr_acc_idx_w_gap.exp: enum_rep
...

Conversely, when I add this test to the test-case:
...
     gdb_test "print enum_with_gaps'enum_rep(lit3)" " = 13" \
 	"enum_rep"
+    gdb_test "print enum_subrange'enum_rep(lit3)" " = 13" \
+	"other enum_rep"
...
the extra test passes with target board cc-with-dwz, but fails with target
board unix.

The problem is here in remove_extra_symbols:
...
  if (symbols_are_identical_enums (syms))
    syms.resize (1);
...
where one of the two identical enums is picked before the enum_rep handling
can resolve lit3 to one of the two.

Fix this by moving the code to ada_resolve_variable.

Tested on x86_64-linux.

Approved-By: Tom Tromey <tom@tromey.com>
PR ada/30726
Bug: https://sourceware.org/bugzilla/show_bug.cgi?id=30726