Testing: Add new tests, and new ways of testing, for floating-point.

- Adds a pragma to see binary output of double values (not portable)
- Print decimals that show more values, but in a portable way
  (lots of portability issues)
- Expand the tests to test more double values

Note: it is quite difficult to have 100% portable tests for floating point.
The current situation works by not printing full precision, and working around
several portability issues.

gtests/AST.FromFile.cpp

@@ -208,6 +208,7 @@ INSTANTIATE_TEST_CASE_P(
         "prepost.frag",
         "runtimeArray.vert",
         "simpleFunctionCall.frag",
+        "stringToDouble.vert",
         "structAssignment.frag",
         "structDeref.frag",
         "structure.frag",