Add While expression mutator

[sidz]

This PR:

• Adds new While expression mutator
• Covered by tests
• Schema needs an update
• Doc PR: Update mutators.md with While mutator site#196

Mutates:

$condition = true;
- while ($condition) {
+ while (false) {

[maks-rafalko]

Cool.

What about do while()? should we add similar mutator?

[sidz]

@maks-rafalko yes we should and I also have a plan to add it but it is not a ZeroIteration mutator. I'm thinking about deprecate @zero_iteration profile in favor of @loop (we also have Loop section in documentation).

But not sure how to achieve this with json schema validator so far. (found that latest shcema (https://json-schema.org/draft/2019-09/release-notes.html#meta-data-vocabulary) has "deprecated" property)

Or we may do it a bit aggressive and just rename zero_iteration profile to loop and release in the next "major".

what do you think @maks-rafalko, @sanmai ?

[sanmai]

I'm for the rename. Next major assumes BC breaks, and that's what it is.

[sidz]

thanks @maks-rafalko , @sanmai