Support for Ternary Operator assignments in var context

What problem are you trying to solve?

While developing #217 I discovered that handling, especially detecting ternary operator assignments, is hard.
With this issue, Rewrite become able to apply ´var´ to ternary operator assignments.

What precondition(s) should be checked before applying this recipe?

var should not be applied to variable declarations where:

• the type of the ternary operator and the left-hand side don't match
• the type is byte or short
• only null is assigned
• the declaration is outside a method declaration

Describe the situation before applying the recipe

class A {
    void foo(String bar) {
        int i1 = bar != null ? 3 : 5;
        Integer i2 = bar != null ? 3 : null;
        Integer i3 = bar == null ? null : bar.lenght();
        Integer i4 = bar != null ? throw new IlligalArgumentExcpetion() : -1;
        int i5 = bar != null ? bar.lenght() : 0;
        float f1 = bar != null ? 3f : 3.5;
    }
}

Describe the situation after applying the recipe

class A {
    void foo(String bar) {
        var i1 = bar != null ? 3 : 5;
        var i2 = bar != null ? 3 : null;
        var i3 = bar == null ? null : bar.lenght();
        var i4 = bar != null ? throw new IlligalArgumentExcpetion() : -1;
        var i5 = bar != null ? bar.lenght() : 0;
        var f1 = bar != null ? 3f : 3.5;
    }
}

Have you considered any alternatives or workarounds?

An alternative would be to skip every ternary operator, this would lead to no 100% local variable type inference for rewrite.

Any additional context

It would be nice to write a separate recipe for this and integrate them later on as global var refactoring.

Are you interested in contributing this recipe to OpenRewrite?

not now.

Begin with the existing var refactoring work referenced in #217 and use the listed ternary examples and preconditions as the behavioral specification. Done means the recipe applies var only to eligible ternary assignments, skips the stated exclusion cases, and verifies the before-and-after outcomes.