Implement a domtree sub-test.

This test verifies the computed dominator tree against annotations.

Move the existing testcases into filetests/ with the new syntax.

filetests/domtree/basic.cton

@@ -0,0 +1,13 @@
+test domtree
+
+function test(i32) {
+    ebb0(v0: i32):
+        jump ebb1     ; dominates: ebb1
+    ebb1:
+        brz v0, ebb3  ; dominates: ebb3
+        jump ebb2     ; dominates: ebb2
+    ebb2:
+        jump ebb3
+    ebb3:
+        return
+}

filetests/domtree/loops.cton

@@ -0,0 +1,20 @@
+test domtree
+
+function test(i32) {
+    ebb0(v0: i32):
+        brz v0, ebb1  ; dominates: ebb1 ebb3 ebb4 ebb5
+        jump ebb2     ; dominates: ebb2
+    ebb1:
+        jump ebb3
+    ebb2:
+        brz v0, ebb4
+        jump ebb5
+    ebb3:
+        jump ebb4
+    ebb4:
+        brz v0, ebb3
+        jump ebb5
+    ebb5:
+        brz v0, ebb4
+        return
+}

filetests/domtree/loops2.cton

@@ -0,0 +1,31 @@
+test domtree
+
+function test(i32) {
+    ebb0(v0: i32):
+        brz v0, ebb1    ; dominates: ebb1 ebb6
+        brnz v0, ebb2   ; dominates: ebb2 ebb9
+        jump ebb3       ; dominates: ebb3
+    ebb1:
+        jump ebb6
+    ebb2:
+        brz v0, ebb4    ; dominates: ebb4 ebb7 ebb8
+        jump ebb5       ; dominates: ebb5
+    ebb3:
+        jump ebb9
+    ebb4:
+        brz v0, ebb4
+        brnz v0, ebb6
+        jump ebb7
+    ebb5:
+        brz v0, ebb7
+        brnz v0, ebb8
+        jump ebb9
+    ebb6:
+        return
+    ebb7:
+        jump ebb8
+    ebb8:
+        return
+    ebb9:
+        return
+}

filetests/domtree/tall-tree.cton

@@ -0,0 +1,33 @@
+test domtree
+
+function test(i32) {
+    ebb0(v0: i32):
+        brz v0, ebb1    ; dominates: ebb1
+        brnz v0, ebb2   ; dominates: ebb2 ebb5
+        jump ebb3       ; dominates: ebb3
+    ebb1:
+        jump ebb4       ; dominates: ebb4
+    ebb2:
+        jump ebb5
+    ebb3:
+        jump ebb5
+    ebb4:
+        brz v0, ebb6    ; dominates: ebb6 ebb10
+        jump ebb7       ; dominates: ebb7
+    ebb5:
+        return
+    ebb6:
+        brz v0, ebb8    ; dominates: ebb11 ebb8
+        brnz v0, ebb9   ; dominates: ebb9
+        jump ebb10
+    ebb7:
+        jump ebb10
+    ebb8:
+        jump ebb11
+    ebb9:
+        jump ebb11
+    ebb10:
+        return
+    ebb11:
+        return
+}

filetests/domtree/wide-tree.cton

@@ -0,0 +1,41 @@
+test domtree
+
+function test(i32) {
+    ebb0(v0: i32):
+        brz v0, ebb13   ; dominates: ebb13
+        jump ebb1       ; dominates: ebb1
+    ebb1:
+        brz v0, ebb2    ; dominates: ebb2 ebb7
+        brnz v0, ebb3   ; dominates: ebb3
+        brz v0, ebb4    ; dominates: ebb4
+        brnz v0, ebb5   ; dominates: ebb5
+        jump ebb6       ; dominates: ebb6
+    ebb2:
+        jump ebb7
+    ebb3:
+        jump ebb7
+    ebb4:
+        jump ebb7
+    ebb5:
+        jump ebb7
+    ebb6:
+        jump ebb7
+    ebb7:
+        brnz v0, ebb8   ; dominates: ebb8 ebb12
+        brz v0, ebb9    ; dominates: ebb9
+        brnz v0, ebb10  ; dominates: ebb10
+        jump ebb11      ; dominates: ebb11
+    ebb8:
+        jump ebb12
+    ebb9:
+        jump ebb12
+    ebb10:
+        brz v0, ebb13
+        jump ebb12
+    ebb11:
+        jump ebb13
+    ebb12:
+        return
+    ebb13:
+        return
+}