This allows removing other clamp macros in various files,
which caused clang-tidy misc-macro-parentheses warnings,
due to their lacks of parens in the macro implementations.
It was also an unneeded duplication of code.

Added asserts to some of the various clamping methods
to confirm that min <= max.  Some of them had these asserts
already, now all do.

Also searched and replaced some identical clamp functions
in various places.

Added unit test.