Perform op stack space check on entering a function

[malcolmstill]

• The idea is rather than potentially perform stack allocation checks for instructions that produce more operands than they consume, calculate the operand stack space requirement for a whole function at parsetime and store this value with the functions metadata
• During execution operand stack overflow checks only occur on function calls, so that instructions like i32.const don't themselves require a check
• Additionally this feels like a move in the direction of the interpreter being a register machine rather than explicitly as stack machine