Replace boost::totally_ordered with explicit operator overloads for SdfHandle

[nvmkuruc]

Description of Change(s)

• Add explicit implementations of operator{<=,>,>=,!=} to SdfHandle when the template parameters match. This mirrors the current behavior inherited from boost::totally_ordered even though operator== and operator< are parameterized to be more general.
• Add doxygen comments so operator!= references operator== and operator{<=,>,>=} reference operator<

Fixes Issue(s)

• boost::totally_ordered can be replaced with explicit operator overloads #2250

• I have verified that all unit tests pass with the proposed changes

• I have submitted a signed Contributor License Agreement

[jesschimein]

Filed as internal issue #USD-8450