message: [XLA] [Docs] Fix typo in operation semantics
  All of `T_N` occurred in the operation semantics doc should be `T_{N-1}` actually, because the first index is 0, and the lengths of the arrays are N.
  The format of the subscript referred to `Map Section`
diff: @@ -393,7 +393,7 @@ Invokes a computation with the given arguments.
  | Arguments | Type | Semantics |
  | ------------- | ---------------------- | ----------------------------------- |
  | `computation` | `XlaComputation` | computation of type `T_0, T_1, ..., |
  -: : : T_N -> S` with N parameters of :
  +: : : T_{N-1} -> S` with N parameters of :
  : : : arbitrary type :
  | `args` | sequence of N `XlaOp`s | N arguments of arbitrary type |
  @@ -1852,9 +1852,9 @@ Applies a reduction function to one or more arrays in parallel.
  | Arguments | Type | Semantics |
  | ------------- | --------------------- | ------------------------------------ |
  -| `operands` | Sequence of N `XlaOp` | N arrays of types `T_0, ..., T_N`. |
  -| `init_values` | Sequence of N `XlaOp` | N scalars of types `T_0, ..., T_N`. |
  -| `computation` | `XlaComputation` | computation of type `T_0, ..., T_N, T_0, ..., T_N ->` `Collate(T_0, ..., T_N)`. |
  +| `operands` | Sequence of N `XlaOp` | N arrays of types `T_0, ..., T_{N-1}`. |
  +| `init_values` | Sequence of N `XlaOp` | N scalars of types `T_0, ..., T_{N-1}`. |
  +| `computation` | `XlaComputation` | computation of type `T_0, ..., T_{N-1}, T_0, ..., T_{N-1} ->` `Collate(T_0, ..., T_{N-1})`. |
  | `dimensions` | `int64` array | unordered array of dimensions to reduce. |
  Where:
  @@ -1862,7 +1862,7 @@ Where:
  * N is required to be greater or equal to 1.
  * All input arrays must have the same dimensions.
  * If `N = 1`, `Collate(T)` is `T`.
  -* If `N > 1`, `Collate(T_0, ..., T_N)` is a tuple of `N` elements of type `T`.
  +* If `N > 1`, `Collate(T_0, ..., T_{N-1})` is a tuple of `N` elements of type `T`.
  The output of the op is `Collate(Q_0, ..., Q_N)` where `Q_i` is an array of type
  `T_i`, the dimensions of which are described below.
  