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

The character after the ending keyword gets blue-painted.

test/asm/interpolate-else.asm

@@ -0,0 +1,13 @@
+def hmm equs "else"
+
+if 1
+	println "yes"
+{hmm}
+	println "no"
+endc
+
+if 0
+	println "NO"
+{hmm}
+	println "YES"
+endc