Add TF_PP_SEQ_FOR_EACH and TF_PP_SEQ_SIZE macros

[nvmkuruc]

Description of Change(s)

This PR adds TF_PP_SEQ_FOR_EACH and TF_PP_SEQ_SIZE which can operate on sequences of parenthetically separated elements. ((x)(y)(z)(w) is a sequence of four elements: x, y, z, and w). Their implementation is similar to their variadic counterparts. They are aided by two new private helpers _TF_PP_SEQ_HEAD and _TF_PP_SEQ_TAIL which can be used to pop the first element off the sequence and apply an operation like a macro.

pyStaticTokens.h requires a global data argument for TF_PP_SEQ_FOR_EACH even though it's generally unused. A future PR will update the static token macros to use TF_PP_SEQ_FOR_EACH.

As the sequence operations support the static token macros, they need to support more elements than their variadic equivalents. (HdTokens currently contains over eighty tokens.) The chosen macro's size limit of 229 is underneath the MSVC's recursive macro limit of 256.

Fixes Issue(s)

• 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-9002