Improve initial load for calculated-expression

[FikriMilano]

Is your feature request related to a problem? Please describe.
The initial load calculated-expression algorithm is very inefficient:

• In a nutshell what it does right now is, for each questionnaireItem, find other questionnaireItems that's using calculated-expressions, then process the calculation.
• Problem is, it's finding ALL calculated-expression for each questionnaireItem, so in one of our forms, we have around 420 normal questionnaireItem, and 80 questionnaireItem with calculated-expression within a form, it will be 33.600(420*80) processes in total. Each calculated-expression is processed 420 times and it's a waste of resource, 1 time is enough. This is a rough estimation, but you see my point.

Describe the solution you'd like
During initial load, directly find all calculated-expression within a form, and process that. It will be 80 process in total.

Describe alternatives you've considered
N/A

Additional context

• The following is total calculation and the time it takes to process it
• Before improvement (~70 seconds)

• After improvement (<1 second)

Would you like to work on the issue?
Yes

[FikriMilano]

@pld @f-odhiambo

[jingtang10]

thanks for raising this issue @FikriMilano and amazing to see the improvements! i'll leave technical comments in the pr itself.