Replace uses of __PRETTY_FUNCTION__ with LLVM_PRETTY_FUNCTION

[GleasonK]

Use LLVM_PRETTY_FUNCTION instead of __PRETTY_FUNCTION__ since it is portable. IREE had reported build errors on windows using __PRETTY_FUNCTION__ for this reason.

Tested debug trace locally, and verified that all uses were changed with the following:

./openxla/stablehlo$ grep -rnw . -e ".*PRETTY.*"
./stablehlo/dialect/ChloBytecode.cpp:43:                      << _EXTRACT_AFTER(LLVM_PRETTY_FUNCTION, func) << '\n')
./stablehlo/dialect/ChloBytecode.cpp:50:                                       << LLVM_PRETTY_FUNCTION << '\n')
./stablehlo/dialect/StablehloBytecode.cpp:42:                      << _EXTRACT_AFTER(LLVM_PRETTY_FUNCTION, func) << '\n')
./stablehlo/dialect/StablehloBytecode.cpp:49:      llvm::errs() << "***Not Implemented: " << LLVM_PRETTY_FUNCTION << '\n')

Closes #147