Add some extra tests

test/files/neg/text-blocks.check

@@ -0,0 +1,13 @@
+text-blocks/Invalid1.java:3: error: illegal text block open delimiter sequence, missing line terminator
+    public static final String badOpeningDelimiter = """non-whitespace
+                                                        ^
+text-blocks/Invalid1.java:3: error: <identifier> expected
+    public static final String badOpeningDelimiter = """non-whitespace
+                                                           ^
+text-blocks/Invalid1.java:5: error: illegal text block open delimiter sequence, missing line terminator
+    """;
+       ^
+text-blocks/Invalid2.java:5: error: unclosed string literal
+      foo"""";
+            ^
+4 errors

test/files/neg/text-blocks/Invalid1.java

@@ -0,0 +1,6 @@
+class Invalid1 {
+
+    public static final String badOpeningDelimiter = """non-whitespace
+      foo
+    """;
+}

test/files/neg/text-blocks/Invalid2.java

@@ -0,0 +1,6 @@
+class Invalid2 {
+
+    // Closing delimiter is first three eligible `"""`, not last
+    public static final String closingDelimiterIsNotScalas = """
+      foo"""";
+}

test/files/run/t12290.check

@@ -42,6 +42,12 @@ ORDER BY "EMP_ID", "LAST_NAME";
     </body>
 </html>
 
+====
+   this line has 4 tabs before it
+ this line has 5 spaces before it and space after it
+ this line has 2 tabs and 3 spaces before it
+  this line has 6 spaces before it
+
 ====
 String text = """
     A text block inside a text block

test/files/run/t12290/Test.scala

@@ -18,6 +18,8 @@ object Test extends App {
   println("====")
   println(valueOf[TextBlocks.html5.type])
   println("====")
+  println(valueOf[TextBlocks.mixedIndents.type])
+  println("====")
   println(valueOf[TextBlocks.code.type])
   println("====")
   println(valueOf[TextBlocks.simpleString.type])

test/files/run/t12290/TextBlocks.java

@@ -55,6 +55,15 @@ class TextBlocks {
                                     </body>
                                 </html>
                                 """;
+
+    // mixed indentation
+		final static String mixedIndents = """
+				\s  this line has 4 tabs before it
+     this line has 5 spaces before it and space after it \u0020 \u000C\u0020 \u001E
+  		 this line has 2 tabs and 3 spaces before it
+\u0020 \u000C\u0020 \u001E this line has 6 spaces before it
+								""";
+
     final static String code =
         """
         String text = \"""