Tightening up the grammar rules. Still Java9.

Update ProfileDescriptor to now parse and output profile. The grammar is asm8080 from grammars-v4, tightened up. The input is the example provided there, truncated to included fewer lines as that causes a null-ptr crash with the older runtime. I verified by modifying the .csproj in /tmp.

--Removing all the test code for Profile = true. See comment here: #3057 (comment)

…other runtimes, a source directory (now antlr4/runtime/CSharp/src), and a test directory (antlr4/runtime/CSharp). In the test area, I added a test for profiling in issue-2593. This test requires the Antlr tool and Antlr C# tool to be build. The path is assumed in a relative path to the test, ../../../../tool/target/antlr4-*-SNAPSHOT-complete.jar, with globbing performed. The test simply checks the return result, output not important. There are no changes to the runtime C# source files other than placing them under src/. Several other build files were changed to reflect the new location of the Antlr C# runtime. I updated the instructions for users on how to build the runtime, including information on checking the environment--now explicitly specified here so people know what to install!