Eliminate gtLsraInfo from GenTree

Eliminate gtLsraInfo from GenTree

Generate TreeNodeInfo into the map when building RefPositions.
Add some new methods and flags for former gtLsraInfo functionality that's used outside of LSRA:
- GenTree::GetRegisterDstCount() (number of registers defined by a node)
- LIR::Flags::RegOptional
- gtDebugFlags::GTF_DEBUG_NODE_LSRA_ADDED

Fix #7255