Add LayerFeaturePermutation

Summary:
Add support for layer attribution via permutation by combining the existing `LayerFeatureAblation` and `FeaturePermutation` attribution classes.

See this [doc](https://docs.google.com/document/d/1HwlBYKOEhguA_9OVrndjuBXE5npr7o6rVntFMF8KDtU/edit#heading=h.fuwkwbjpq8z) for design.

Unit tests will be added in a follow-up diff from yucu.

Differential Revision: D54551200

fbshipit-source-id: 419fd5a2ba0129aae9eb90e8af681721483e4ea2

Author: Marcio Porto

captum/attr/__init__.py

@@ -21,6 +21,9 @@
     LayerDeepLiftShap,
 )
 from captum.attr._core.layer.layer_feature_ablation import LayerFeatureAblation  # noqa
+from captum.attr._core.layer.layer_feature_permutation import (  # noqa
+    LayerFeaturePermutation,
+)
 from captum.attr._core.layer.layer_gradient_shap import LayerGradientShap  # noqa
 from captum.attr._core.layer.layer_gradient_x_activation import (  # noqa
     LayerGradientXActivation,

captum/attr/_core/feature_permutation.py

@@ -255,6 +255,10 @@ def attribute(  # type: ignore
             >>> attr = feature_perm.attribute(input, target=1,
             >>>                               feature_mask=feature_mask)
         """
+        # Remove baselines from kwargs if provided so we don't specify this field
+        # twice in the FeatureAblation.attribute call below.
+        if isinstance(kwargs, dict) and "baselines" in kwargs:
+            del kwargs["baselines"]
         return FeatureAblation.attribute.__wrapped__(
             self,
             inputs,

captum/attr/_core/layer/layer_feature_ablation.py

@@ -288,10 +288,10 @@ def forward_hook(module, inp, out=None):
                 else inputs + layer_eval_len
             )
 
-            ablator = FeatureAblation(layer_forward_func)
+            attributor = self.attributor(layer_forward_func)
 
-            layer_attribs = ablator.attribute.__wrapped__(
-                ablator,  # self
+            layer_attribs = attributor.attribute.__wrapped__(
+                attributor,  # self
                 layer_eval,
                 baselines=layer_baselines,
                 additional_forward_args=all_inputs,
@@ -300,3 +300,7 @@ def forward_hook(module, inp, out=None):
             )
             _attr = _format_output(len(layer_attribs) > 1, layer_attribs)
         return _attr
+
+    @property
+    def attributor(self):
+        return FeatureAblation

captum/attr/_core/layer/layer_feature_permutation.py

@@ -0,0 +1,15 @@
+#!/usr/bin/env python3
+from captum.attr._core.feature_permutation import FeaturePermutation
+from captum.attr._core.layer.layer_feature_ablation import LayerFeatureAblation
+
+
+class LayerFeaturePermutation(LayerFeatureAblation):
+    r"""
+    A perturbation based approach to computing layer attribution similar to
+    LayerFeatureAblation, but using FeaturePermutation under the hood instead
+    of FeatureAblation.
+    """
+
+    @property
+    def attributor(self):
+        return FeaturePermutation