[rtextures] Adding ImageDrawLineEx function

[Bigfoot71]

Description

I propose adding the ImageDrawLineEx function with the same signature as DrawLineEx from rshapes.c, enabling line rendering with specified thickness on an Image. This might not be the most efficient method used here, but it is the most concise, understandable, and maintainable, and it is fully functional.

In this PR, I have also revised the ImageDrawLine function to be shorter and more readable in my opinion, thus more maintainable as well. It avoids the use of float types entirely, performing all calculations using integers and utilizing a bit-shift trick for slope calculation.

Additionally, I took the liberty of modifying the ImageDrawLineV function to round input coordinates to the nearest integer using (int)(xfloat + 0.5f), which I find preferable. However, I can revert this change to the original state if there are objections to this approach.

Basic Example

#include "raylib.h"
#include <math.h>

int main(void)
{
    InitWindow(800, 600, "Lines");

    Image image = GenImageColor(800, 600, BLACK);
    Texture texture = LoadTextureFromImage(image);

    Vector2 p1 = { 0 };
    Vector2 p2 = { 0 };

    while (!WindowShouldClose())
    {
        BeginDrawing();

        ImageClearBackground(&image, BLACK);

        p1.x = 400 + cosf(GetTime())*1000;
        p1.y = 300 - sinf(GetTime())*1000;
        p2.x = 400 + cosf(GetTime() + PI)*1000;
        p2.y = 300 - sinf(GetTime() + PI)*1000;

        ImageDrawLineEx(&image, p1, p2, 8, BLUE);
        ImageDrawLineEx(&image, (Vector2) { 0, 0 }, (Vector2) { 800, 600 }, 8, RED);
        ImageDrawLineEx(&image, (Vector2) { 800, 0 }, (Vector2) { 0, 600 }, 8, RED);

        UpdateTexture(texture, image.data);
        DrawTexture(texture, 0, 0, WHITE);

        EndDrawing();
    }

    CloseWindow();

    return 0;
}

GIF Example

[raysan5]

@Bigfoot71 Nice! Thanks for the addition!