[rtextures] Fix LoadImageAnimFromMemory() warning for fileData

[ghost]

Changes

1. Fixes the warning below (introduced after #3681):

rtextures.c: In function ‘LoadImageAnimFromMemory’:
rtextures.c:472:46: warning: pointer targets in passing argument 2 of ‘LoadImageFromMemory’ differ in signedness [-Wpointer-sign]
  472 |         image = LoadImageFromMemory(fileType,fileData,dataSize);
      |                                              ^~~~~~~~
      |                                              |
      |                                              const char *
In file included from rtextures.c:64:
raylib.h:1305:76: note: expected ‘const unsigned char *’ but argument is of type ‘const char *’
 1305 | RLAPI Image LoadImageFromMemory(const char *fileType, const unsigned char *fileData, int dataSize);      // Load image from memory buffer, fileType refers to extension: i.e. '.png'
      |                                                       ~~~~~~~~~~~~~~~~~~~~~^~~~~~~~
In file included from rtextures.c:216:

2. Does that by changing const char *fileData to const unsigned char *fileData (R446).

3. Adds LoadImageAnimFromMemory() to raylib.h (R1305) that was missing.

Edits:

• 1. added line marks.
• 2. added function to raylib.h.

[raysan5]

@ubkp thanks for the review!