Support dnggainmap (embedded correction) for Bayer files (#6382)

* dng gainmap support, #6379
* dng GainMap: control sensitivity of checkbox, #6379
* dng GainMap: partial paste
* dng GainMap: moved isGainMapSupported() from dcraw.h to dcraw.cc
* RawImageSource::applyDngGainMap: small speedup
* Change GUI to separate gainmap from other flat-field; also reorder checkbox

Co-authored-by: Thanatomanic <6567747+Thanatomanic@users.noreply.github.com>

rtengine/dnggainmap.h

@@ -0,0 +1,43 @@
+/*
+ *  This file is part of RawTherapee.
+ *
+ *  Copyright (c) 2021 Ingo Weyrich <heckflosse67@gmx.de>
+ *
+ *  RawTherapee is free software: you can redistribute it and/or modify
+ *  it under the terms of the GNU General Public License as published by
+ *  the Free Software Foundation, either version 3 of the License, or
+ *  (at your option) any later version.
+ *
+ *  RawTherapee is distributed in the hope that it will be useful,
+ *  but WITHOUT ANY WARRANTY; without even the implied warranty of
+ *  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ *  GNU General Public License for more details.
+ *
+ *  You should have received a copy of the GNU General Public License
+ *  along with RawTherapee.  If not, see <https://www.gnu.org/licenses/>.
+ */
+
+#pragma once
+
+#include <cstdint>
+#include <vector>
+
+struct GainMap
+{
+    std::uint32_t Top;
+    std::uint32_t Left;
+    std::uint32_t Bottom;
+    std::uint32_t Right;
+    std::uint32_t Plane;
+    std::uint32_t Planes;
+    std::uint32_t RowPitch;
+    std::uint32_t ColPitch;
+    std::uint32_t MapPointsV;
+    std::uint32_t MapPointsH;
+    double MapSpacingV;
+    double MapSpacingH;
+    double MapOriginV;
+    double MapOriginH;
+    std::uint32_t MapPlanes;
+    std::vector<float> MapGain;
+};