transform: copy and accessible versions

* src/tgbaalgos/mask.cc, src/tgbaalgos/mask.hh: Rename transform_mask
to accessible_mask. Add Copy version and use it in mask_keep_states().
* src/tgbatest/maskkeep.test: Update.

src/tgbatest/maskkeep.test

@@ -48,7 +48,7 @@ EOF
 
 cat >expect1 <<EOF
 HOA: v1
-States: 1
+States: 4
 Start: 0
 AP: 0
 acc-name: generalized-Buchi 2
@@ -56,6 +56,25 @@ Acceptance: 2 Inf(0)&Inf(1)
 properties: trans-labels explicit-labels state-acc deterministic
 --BODY--
 State: 0
+State: 1
+State: 2
+State: 3
+--END--
+EOF
+
+cat >expect2 <<EOF
+HOA: v1
+States: 4
+Start: 1
+AP: 0
+acc-name: generalized-Buchi 2
+Acceptance: 2 Inf(0)&Inf(1)
+properties: trans-labels explicit-labels state-acc deterministic
+--BODY--
+State: 0
+State: 1
+State: 2
+State: 3
 --END--
 EOF
 
@@ -63,11 +82,11 @@ run 0 ../../bin/autfilt --keep-states=0 input1 -H >output
 diff output expect1
 
 run 0 ../../bin/autfilt --keep-states=1 input1 -H >output
-diff output expect1
+diff output expect2
 
 cat >expect3 <<EOF
 HOA: v1
-States: 3
+States: 4
 Start: 0
 AP: 2 "a" "b"
 acc-name: generalized-Buchi 2
@@ -81,22 +100,27 @@ State: 1
 [0] 2
 State: 2
 [1] 1
+State: 3
 --END--
 EOF
 
 cat >expect4 <<EOF
 HOA: v1
-States: 2
-Start: 0
+States: 4
+Start: 1
 AP: 2 "a" "b"
 acc-name: generalized-Buchi 2
 Acceptance: 2 Inf(0)&Inf(1)
-properties: trans-labels explicit-labels state-acc deterministic
+properties: trans-labels explicit-labels trans-acc
 --BODY--
 State: 0
-[0] 1
+[0] 1 {0}
+[1] 2 {1}
 State: 1
-[1] 0
+[0] 2
+State: 2
+[1] 1
+State: 3
 --END--
 EOF