feat(lint): created local rule to use isNullish and nonNullish

[AntonioVentilii-DFINITY]

Motivation

We would like to enforce the usage of functions isNullish and nonNullish in the code whenever possible. As first step we look for instances of comparing a variable with undefined and/or null.

Changes

• Created custom local lint rule for isNullish usage.
• Created custom local lint rule for nonNullish usage.
• Create exceptions where necessary.
• Fix issues created by new rules.

Tests

It raised issues, correctly, and we fixed it.

[AntonioVentilii-DFINITY]

Clean PR:

• feat(lint): created local rule to use isNullish and nonNullish #2553