Cleanup: move Alembic, AVI, Collada, and USD to source/blender/io

This moves the `alembic`, `avi`, `collada`, and `usd` modules into a common
`io` directory.

This also cleans up some `#include "../../{somedir}/{somefile}.h"` by
adding `../../io/{somedir}` to `CMakeLists.txt` and then just using
`#include "{somefile}.h"`.

No functional changes.

source/blender/io/avi/intern/avi_intern.h

@@ -0,0 +1,65 @@
+/*
+ * This program 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 2
+ * of the License, or (at your option) any later version.
+ *
+ * This program 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 this program; if not, write to the Free Software Foundation,
+ * Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301, USA.
+ *
+ * The Original Code is Copyright (C) 2001-2002 by NaN Holding BV.
+ * All rights reserved.
+ */
+
+/** \file
+ * \ingroup avi
+ */
+
+#ifndef __AVI_INTERN_H__
+#define __AVI_INTERN_H__
+
+#include <stdio.h> /* for FILE */
+
+unsigned int GET_FCC(FILE *fp);
+unsigned int GET_TCC(FILE *fp);
+
+#define PUT_FCC(ch4, fp) \
+  { \
+    putc(ch4[0], fp); \
+    putc(ch4[1], fp); \
+    putc(ch4[2], fp); \
+    putc(ch4[3], fp); \
+  } \
+  (void)0
+
+#define PUT_FCCN(num, fp) \
+  { \
+    putc((num >> 0) & 0377, fp); \
+    putc((num >> 8) & 0377, fp); \
+    putc((num >> 16) & 0377, fp); \
+    putc((num >> 24) & 0377, fp); \
+  } \
+  (void)0
+
+#define PUT_TCC(ch2, fp) \
+  { \
+    putc(ch2[0], fp); \
+    putc(ch2[1], fp); \
+  } \
+  (void)0
+
+void *avi_format_convert(
+    AviMovie *movie, int stream, void *buffer, AviFormat from, AviFormat to, size_t *size);
+
+int avi_get_data_id(AviFormat format, int stream);
+int avi_get_format_type(AviFormat format);
+int avi_get_format_fcc(AviFormat format);
+int avi_get_format_compression(AviFormat format);
+
+#endif