Reduce number of times we compute price from ticks in AddLiquidityActionCard

[haydenshively]

I see your reasoning, but what if we did the following:

define the following above the input:

const lowerStepperInputValue = isToken0Selected ? prices?.[0] : prices?.[1];
const upperStepperInputValue = isToken0Selected ? prices?.[1] : prices?.[0];

this gives us either null if the prices are not defined, or the corresponding price for each input if the prices are defined.

Then, we switch the ternary operator to use lowerStepperInputValue == null and upperStepperInputValue == null respectively and make the else case equal to lowerStepperInputValue.toString(10) and upperStepperInputValue.toString(10) respectively.

While this may look like more code, it requires fewer calculations and thus I feel is better and more performant.

Originally posted by @IanWoodard in #134 (comment)