swift

4094b76e - [NFC] [AutoDiff] Rename `AutoDiffFunction` to `DifferentiableFunction`. (#27471)

[NFC] [AutoDiff] Rename `AutoDiffFunction` to `DifferentiableFunction`. (#27471) Rename: - `AutoDiffFunctionExpr` -> `DifferentiableFunctionExpr` - `AutoDiffFunctionExtractOriginalExpr` -> `DifferentiableFunctionExtractOriginalExpr` - `AutoDiffFunctionInst` -> `DifferentiableFunctionInst` - `AutoDiffFunctionExtractInst` -> `DifferentiableFunctionExtractInst` - `AutoDiffFunctionExtractee` -> `DifferentiableFunctionExtractee` "Differentiable function" is a clearer name because these expressions and instructions involve constructing/extracting from differentiable functions. "AutoDiff" (automatic differentiation) is an internal detail. Update docs, comments, and tests.