Adding BASISU_DISABLE_ANDROID_ASTC_DECOMP cmake option: if 1, the android ASTC decoder .cpp file is entirely eliminated and we emulate its functionality internally.

diff --git a/encoder/3rdparty/android_astc_decomp.h b/encoder/3rdparty/android_astc_decomp.h
deleted file mode 100644
index cfa96aa..0000000
--- a/encoder/3rdparty/android_astc_decomp.h
+++ /dev/null

@@ -1,47 +0,0 @@
-// File: android_astc_decomp.h
-#ifndef _TCUASTCUTIL_HPP
-#define _TCUASTCUTIL_HPP
-/*-------------------------------------------------------------------------
- * drawElements Quality Program Tester Core
- * ----------------------------------------
- *
- * Copyright 2016 The Android Open Source Project
- *
- * Licensed under the Apache License, Version 2.0 (the "License");
- * you may not use this file except in compliance with the License.
- * You may obtain a copy of the License at
- *
- *      http://www.apache.org/licenses/LICENSE-2.0
- *
- * Unless required by applicable law or agreed to in writing, software
- * distributed under the License is distributed on an "AS IS" BASIS,
- * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
- * See the License for the specific language governing permissions and
- * limitations under the License.
- * 
- * 4/3/2026: Set BASISU_DISABLE_ANDROID_ASTC_DECOMP to 1 to completely disable this code and redirect all calls to our internal ASTC decoder.
- *
- *//*!
- * \file
- * \brief ASTC Utilities.
- *//*--------------------------------------------------------------------*/
-
-#include <vector>
-#include <stdint.h>
-
-namespace basisu_astc
-{
-namespace astc
-{
-
-// Unpacks a single ASTC block to pDst
-// If isSRGB is true, the spec requires the decoder to scale the LDR 8-bit endpoints to 16-bit before interpolation slightly differently,
-// which will lead to different outputs. So be sure to set it correctly (ideally it should match whatever the encoder did).
-bool decompress_ldr(uint8_t* pDst, const uint8_t* data, bool isSRGB, int blockWidth, int blockHeight);
-bool decompress_hdr(float* pDstRGBA, const uint8_t* data, int blockWidth, int blockHeight);
-bool is_hdr(const uint8_t* data, int blockWidth, int blockHeight, bool& is_hdr_flag);
-
-} // astc
-} // basisu
-
-#endif