Avoid false positive "possibly unbound" #4087
Description
When variables are conditionally declared, then pyright may show "possibly unbound" error, even though ideally it should be able to infer that the variable won't be unbound.
DEFINE_X = True
if(DEFINE_X):
x = 3
# ...
# Code that does not touch DEFINE_X
# ...
if(DEFINE_X):
y = x + 3 # This line is highlighted as "x possibly unbound"
# There is enough information in the code to ensure that
# x is not unbound at this time. Perhaps such false positive
# error messages can be avoided?