Cleanups and additional tests to improve test coverage (#2852)

* disable builds of the StructChecker code by default

* operator"" _smarts() doesn't need to catch sanitization errors

* remove unused function

* turn back on some tests that shouldn't have been disabled

* Remove unused code from SMARTS parser and simplify a bit

SmilesParseOps::AddFragToMol is now used only from the SMARTS parser, so we can simplify the API

* Removes obsolete special case code for SMARTS

This was relevant when organic atoms in SMARTS queries were stored as two-part queries.

* improve SMARTS testing

make sure we can generate SMARTS from all the examples and then parse that again.

* Fixes #2814

* Fixes #2815

* some additional smarts tests to improve coverage

* test copy ctor and getPos

* remove obsolete test_list files

* include tests for the morgan invariant generators

* more cleanups and coverage improvements

* remove files that were mistakenly added

Code/SimDivPickers/Wrap/test_list.py

@@ -1,9 +0,0 @@
-tests = [("python", "testPickers.py", {}), ("python", "testMaxMin.py", {})]
-
-longTests = []
-
-if __name__ == '__main__':
-  import sys
-  from rdkit import TestRunner
-  failed, tests = TestRunner.RunScript('test_list.py', 0, 1)
-  sys.exit(len(failed))