Add more tests of lexer's skipToLeadingKeyword behavior (#1971)

The character after the ending keyword gets blue-painted.

test/asm/expansion-after-end.asm

@@ -0,0 +1,25 @@
+DEF x = 0
+DEF s EQUS "\nprintln \"lol\", x\ndef x += 1"
+
+if 0
+	println "no"
+endc{#s}
+
+if 1
+	println "yes"
+else{#s}
+	println "nope"
+endc{#s}
+
+rept 0
+	println "no way"
+endr{#s}
+
+println "x = ", x
+
+MACRO m
+	if 0
+		println "no how"
+	endc\1
+ENDM
+m \nprintln "haha"