📎 `useNullishCoalescing`: suggest `??=` for logical OR assignment (`||=`)

[pkallos]

Description

Follow-up to #8043 / PR #8952.

Extend useNullishCoalescing to detect ||= assignment expressions where the left-hand side is possibly nullish and suggest rewriting them as ??=.

Pattern to detect:

• a ||= b -> a ??= b

The existing type-eligibility and safety logic from the || -> ?? check applies directly here. The main work is adding a new query target for JsAssignmentExpression with the ||= operator, reusing is_possibly_nullish and is_safe_type_for_replacement to gate the diagnostic and fix.

The fix itself is a straightforward token replacement of ||= with ??=, same approach as the existing || -> ?? fix.

References:

• ESLint rule: AssignmentExpression[operator = "||="] visitor in prefer-nullish-coalescing