Replace `require(x != null)` with `requireNotNull(x)`

[3flex]

Expected Behavior of the rule

When detekt comes across a require call that is just checking that a property is not null, suggest replacing with requireNotNull.

Context

#2336

And also:

detekt/detekt-core/src/main/kotlin/io/gitlab/arturbosch/detekt/core/KtFileModifier.kt

Line 27 in 102c28d

require(lineSeparator != null) {

[maltaisn]

I believe this also applies to checkNotNull.

[schalkms]

I think this rule belongs to the style ruleset.