boost::in_place can be replaced by emplace methods

[nvmkuruc]

Description of Issue

TfType and UsdStage use boost::in_place to initialize boost::optional instances. The STL has introduced emplace as the standard way to do in_place initialization. As recent versions of boost::optional support emplace, boost::in_place usage can be removed. Doing so will make it easier to swap out boost::optional for std::optional in the future and removes another boost dependency.

Steps to Reproduce

N/A

System Information (OS, Hardware)

N/A

Package Versions

N/A

Build Flags

N/A

[nvmkuruc]

I have a fix.

[sunyab]

Filed as internal issue #USD-8027