Disallow illegal usage of expression groups in text Ion 1.1

[tgregg]

IonRawTestReaderTest_1_1.validValuesInvocations contains three tests that should be invalid:

• (:values (:: (:: 0) (:values (:: 1)))) - Nested expression groups are not allowed (cannot be represented in binary).
• (:values (:: 0) (:values (:: 1))) - Rest parameter may contain either a single expression group or a sequence of non-group expressions.
• (:1 (:: (:: 0) (:1 (:: 1)))) - Nested expression groups are not allowed (cannot be represented in binary).

For now they're commented out, but to resolve this issue they should be moved to IonRawTestReaderTest_1_1.invalidExpressionSyntax, with the necessary validation added to the source to reject them.