Fix broken test runner (!).

If a test expected an error and found at least one, it would not fail
on any other expected errors that didn't occur.

Also, some tests were expecting a compile time error message even though
the test script doesn't validate those (yet).

The test function was getting monolithic, so I went ahead and split it
into a separate little class.

test/language/function/newline_in_expression_block.wren

@@ -1,5 +1,2 @@
-new Fn { IO.print("ok") // expect error
-}.call() // expect error
-
-// The second error is cascaded here. If it starts failing, just remove that
-// expectation.
+Fn.new { IO.print("ok") // expect error
+}.call()

test/language/number/hex_too_large.wren

@@ -1 +1 @@
-var x = 0x999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999 // expect error: Error: Number literal was too large.
+var x = 0x999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999 // expect error

test/language/number/literal_too_large.wren

@@ -1 +1 @@
-var x = 999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999 // expect error: Error: Number literal was too large.
+var x = 999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999999 // expect error