copying "cross_validation_helper" code from ax.plot (facebook#2249)

Summary:

To prepare of creating the "CrossValidationPlot" module, this change imports the dependent code from "ax.plots". 
It also cleans up the original code by breaking it apart into different helper files, and trimming out methods which are not used to create this plot. Some new unit tests are being added as well.

Differential Revision: D54495372

ax/analysis/helpers/color_helpers.py

@@ -0,0 +1,33 @@
+#!/usr/bin/env python3
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+
+from numbers import Real
+from typing import List, Tuple
+
+# type aliases
+TRGB = Tuple[Real, ...]
+
+
+def rgba(rgb_tuple: TRGB, alpha: float = 1) -> str:
+    """Convert RGB tuple to an RGBA string."""
+    return "rgba({},{},{},{alpha})".format(*rgb_tuple, alpha=alpha)
+
+
+def plotly_color_scale(
+    list_of_rgb_tuples: List[TRGB],
+    reverse: bool = False,
+    alpha: float = 1,
+) -> List[Tuple[float, str]]:
+    """Convert list of RGB tuples to list of tuples, where each tuple is
+    break in [0, 1] and stringified RGBA color.
+    """
+    if reverse:
+        list_of_rgb_tuples = list_of_rgb_tuples[::-1]
+    return [
+        (round(i / (len(list_of_rgb_tuples) - 1), 3), rgba(rgb))
+        for i, rgb in enumerate(list_of_rgb_tuples)
+    ]

ax/analysis/helpers/constants.py

@@ -0,0 +1,97 @@
+# Copyright (c) Meta Platforms, Inc. and affiliates.
+#
+# This source code is licensed under the MIT license found in the
+# LICENSE file in the root directory of this source tree.
+
+import enum
+
+# Constants used for numerous plots
+CI_OPACITY = 0.4
+DECIMALS = 3
+Z = 1.96
+
+
+# color constants used for plotting
+class COLORS(enum.Enum):
+    STEELBLUE = (128, 177, 211)
+    CORAL = (251, 128, 114)
+    TEAL = (141, 211, 199)
+    PINK = (188, 128, 189)
+    LIGHT_PURPLE = (190, 186, 218)
+    ORANGE = (253, 180, 98)
+
+
+# colors to be used for plotting discrete series
+# pyre-fixme[5]: Global expression must be annotated.
+DISCRETE_COLOR_SCALE = [
+    COLORS.STEELBLUE.value,
+    COLORS.CORAL.value,
+    COLORS.PINK.value,
+    COLORS.LIGHT_PURPLE.value,
+    COLORS.ORANGE.value,
+    COLORS.TEAL.value,
+]
+
+# 11-class PiYG from ColorBrewer (for contour plots)
+GREEN_PINK_SCALE = [
+    (142, 1, 82),
+    (197, 27, 125),
+    (222, 119, 174),
+    (241, 182, 218),
+    (253, 224, 239),
+    (247, 247, 247),
+    (230, 245, 208),
+    (184, 225, 134),
+    (127, 188, 65),
+    (77, 146, 33),
+    (39, 100, 25),
+]
+GREEN_SCALE = [
+    (247, 252, 253),
+    (229, 245, 249),
+    (204, 236, 230),
+    (153, 216, 201),
+    (102, 194, 164),
+    (65, 174, 118),
+    (35, 139, 69),
+    (0, 109, 44),
+    (0, 68, 27),
+]
+BLUE_SCALE = [
+    (255, 247, 251),
+    (236, 231, 242),
+    (208, 209, 230),
+    (166, 189, 219),
+    (116, 169, 207),
+    (54, 144, 192),
+    (5, 112, 176),
+    (3, 78, 123),
+]
+# 24 Class Mixed Color Palette
+# Source: https://graphicdesign.stackexchange.com/a/3815
+MIXED_SCALE = [
+    (2, 63, 165),
+    (125, 135, 185),
+    (190, 193, 212),
+    (214, 188, 192),
+    (187, 119, 132),
+    (142, 6, 59),
+    (74, 111, 227),
+    (133, 149, 225),
+    (181, 187, 227),
+    (230, 175, 185),
+    (224, 123, 145),
+    (211, 63, 106),
+    (17, 198, 56),
+    (141, 213, 147),
+    (198, 222, 199),
+    (234, 211, 198),
+    (240, 185, 141),
+    (239, 151, 8),
+    (15, 207, 192),
+    (156, 222, 214),
+    (213, 234, 231),
+    (243, 225, 235),
+    (246, 196, 225),
+    (247, 156, 212),
+]