src/vs/workbench/contrib/notebook/common/model/notebookCellTextModel.ts/NotebookCellTextModel/getTextBufferHash
class NotebookCellTextModel:	getTextBufferHash() {
		if (this._textBufferHash !== null) {
			return this._textBufferHash;
		}

		const shaComputer = new StringSHA1();
		const snapshot = this.textBuffer.createSnapshot(false);
		let text: string | null;
		while ((text = snapshot.read())) {
			shaComputer.update(text);
		}
		this._textBufferHash = shaComputer.digest();
		return this._textBufferHash;
	}