Function checkFootnoteExists

checkFootnoteExists(
    plugin: default,
    targetFilePath: string,
    sourceFilePath: string,
    createIfNotExist?: boolean,
): Promise<string | null>
Check if a footnote that referencing the source file already exists in the target file,

create a new footnote if it doesn't exist and creation is requested
Parameters
- plugin: default
  The EquationCitator plugin instance
- targetFilePath: string
  The target file path where the footnote will be searched or created
- sourceFilePath: string
  The source file path that is referenced by the footnote
- createIfNotExist: boolean = false
  Whether to create a new footnote if it doesn't exist, defaults to false
Returns Promise<string | null>
Returns the existing footnote number or the newly created footnote number, or null if not found and not created
- Defined in src/utils/core/footnote_utils.tsx:19