Refactor getSlotted dom utility method

[driskull]

Description

Update the getSlotted method signature to match below.

export function getSlotted<T extends Element = Element>(element: Element, options: GetSlottedOptions & { all: true }): T[];
export function getSlotted<T extends Element = Element>(element: Element, options?: GetSlottedOptions): T[];
export function getSlotted<T extends Element = Element>(element: Element, slotName: string | string[], options: GetSlottedOptions & { all: true }): T[];
export function getSlotted<T extends Element = Element>(element: Element, slotName: string | string[], options?: GetSlottedOptions): T[];
export function getSlotted<T extends Element = Element>(
  element: Element,
  slotNameOrOptions: string | string[] | GetSlottedOptions,
  optionsOrUndefined?: GetSlottedOptions): (T | null) | T[] { /* ... */ }

Proposed Advantages

Allows the slotName parameter to be optional.

Relevant Info

#3788 (comment)

Which Component

N/A

[geospatialem]

Closing, will instead work on removal with #6059.