Add separate variants to `ObjectPropertyKind` for methods, getters and setters

https://github.com/oxc-project/oxc/issues/7175 demonstrates that it's easy to confuse a function which is the property value of an object expression with an object method. i.e. to conflate these 2:

obj = {
    foo() {}
};

obj = {
    foo: function() {}
};

We could avoid this confusing by changing ObjectPropertyKind to have separate variants for methods, getters and setters.

Current:

pub enum ObjectPropertyKind<'a> {
    // This variant can be either a property or a method
    ObjectProperty(Box<'a, ObjectProperty<'a>>),
    SpreadProperty(Box<'a, SpreadElement<'a>>),
}

Proposed:

pub enum ObjectPropertyKind<'a> {
    ObjectProperty(Box<'a, ObjectProperty<'a>>),
    SpreadProperty(Box<'a, SpreadElement<'a>>),
    Method(Box<'a, ObjectMethod<'a>>),
    Getter(Box<'a, ObjectMethod<'a>>),
    Setter(Box<'a, ObjectMethod<'a>>),
}

pub struct ObjectProperty<'a> {
    pub span: Span,
    // pub kind: PropertyKind, <-- removed
    pub key: PropertyKey<'a>,
    pub value: Expression<'a>,
    pub init: Option<Expression<'a>>, // for `CoverInitializedName`
    // pub method: bool, <-- removed
    pub shorthand: bool,
    pub computed: bool,
}

pub struct ObjectMethod<'a> {
    pub span: Span,
    pub key: PropertyKey<'a>,
    pub func: Function<'a>,
    pub computed: bool,
}

Read the ObjectPropertyKind, ObjectProperty, and ObjectMethod definitions shown in the issue, then trace how the existing variants and fields are constructed and consumed. Done means methods, getters, setters, property values, and spread properties have the distinct representations proposed, with the removed fields no longer needed.