_getGraphemeAwarePosition() {
        const { lineNumber, column } = this._position;
        const lineContent = this._context.viewModel.getLineContent(lineNumber);
        const [startOffset, endOffset] = strings.getCharContainingOffset(lineContent, column - 1);
        return [new Position(lineNumber, startOffset + 1), lineContent.substring(startOffset, endOffset)];
    }
If `this._position` is inside a grapheme, returns the position where the grapheme starts.
Also returns the next grapheme.