Alternative fix for unused functions warnings on stb_truetype.h (and …

[ghost]

…stb_image.h)

As mentioned on #3235, submiting this for consideration since it could be an alternative way to workaround the unused functions warnings on stb_truetype.h (and stb_image.h).

Adds a void unused_stb_truetype(void) at the end of stb_truetype.h (R4967-R5000) and void unused_stb_image(void) at the end of stb_image.h (R7761-R7767) with the list of unused functions.

Downsides:

• Has to be readded when stb_truetype.h and stb_image are updated;
• Has to be manually populated;
• Can be a bit verbose if there are too many unused functions (like this case on stb_truetype.h).

Upsides:

• Fairly benign (shouldn't interfere or affect in any way the libraries operation, nor return anything if ever called);
• Fairly simple and contained (just a single function with the list of unused functions in the end of the file it directly relates to);
• Platform agnostic;
• Doesn't affect the building system;
• Maintains the warnings active, which, IMHO, are helpful.

Since it's an alternative method, this PR also reverts #3235 (rtext.c L74-L77, L86-L88) (rtexture.c L141-L144, L154-L156, L165-L168, L174-L176).

Tested successfully on PLATFORM_DESKTOP on Linux (Linux Mint 21.1 x86_64) and PLATFORM_WEB.

I think @ashn-dot-dev solution is pretty good. Just submiting this because it looked like an option worth testing.

Edit: added line marks.

[ghost]

Closed in accordance with #3235 (comment).

[raysan5]

@ubkp thanks for the review and excuse the late response here.