Get the withdrawal tokens given a number of vaultTokens and the desired withdraw proportions return the withdrawal tokens.
How many out of sum(withdrawalWeights) should the user get of this token? An array of [[1,3], [4]] implies [[1/8 = 12.5%, 3/8 = 37.5%], [4/8 = 50%]]
Get the withdrawal tokens given a number of vaultTokens and the desired withdraw proportions return the withdrawal tokens.