Sync repository with ANTLR 4.7.2

[KvanTTT]

There are many useful improvements and fixes, including the following ones:

• Full Unicode support
• Additional lexer checks

[sharwell]

This is a work in progress:

1. Finalizing the ANTLR 4.6.x work
   1. The new code generator (port of the original ANTLR 4 Tool to C#) needs to be verified in additional scenarios
   2. Additional validation for cross-platform code generation scenarios
2. New 4.7.x work
   1. Revert all breaking API changes (the C# releases here do not allow breaking API changes, so the new functionality will need to be provided with full compatibility)
   2. Port the runtime changes
   3. Port the tool changes to the new code generator

Over the past few weeks I made substantial progress in finalizing the 4.6.x releases, so 4.7.x should not be far off. Most of the work for reverting breaking changes was completed when I updated the optimized Java runtime for 4.7.1.

Also, keep in mind that my 4.6.x releases already contain a number of the bug fixes that went into 4.7.x so the difference is not as large as one might expect.

[lextm]

Related to #381