src/vs/editor/common/languages/languageConfigurationRegistry.ts/getIndentationAtPosition
export function getIndentationAtPosition(model: ITextModel, lineNumber: number, column: number): string {
	const lineText = model.getLineContent(lineNumber);
	let indentation = strings.getLeadingWhitespace(lineText);
	if (indentation.length > column - 1) {
		indentation = indentation.substring(0, column - 1);
	}
	return indentation;
}