message: IntervalCollection fuzz: allow insert at end of string
diff: @@ -149,18 +149,18 @@ function makeOperationGenerator(optionsParam?: OperationGenerationConfig): Gener
  }
  // All subsequent helper functions are generators; note that they don't actually apply any operations.
  - function position({ random, sharedString }: ClientOpState): number {
  + function startPosition({ random, sharedString }: ClientOpState): number {
  return random.integer(0, Math.max(0, sharedString.getLength() - 1));
  }
  function exclusiveRange(state: ClientOpState): RangeSpec {
  - const start = position(state);
  + const start = startPosition(state);
  const end = state.random.integer(start + 1, state.sharedString.getLength());
  return { start, end };
  }
  function inclusiveRange(state: ClientOpState): RangeSpec {
  - const start = position(state);
  + const start = startPosition(state);
  const end = state.random.integer(start, Math.max(start, state.sharedString.getLength() - 1));
  return { start, end };
  }
  @@ -200,7 +200,7 @@ function makeOperationGenerator(optionsParam?: OperationGenerationConfig): Gener
  const { random, sharedString } = state;
  return {
  type: "addText",
  - index: position(state),
  + index: random.integer(0, sharedString.getLength()),
  content: random.string(random.integer(0, options.maxInsertLength)),
  stringId: sharedString.id,
  };
  