Fix Texture2D::Create(...) to generate correct internal image buffer size

[JeanPhilippeKernel]

Texture2D struct has public APIs that help the creation of monochrome texture.

• Create (uint32_t width, uint32_t height)
• Create (uint32_t width, uint32_t height, float r, float g, float b, float a)

The current implementation of those methods uses a fixed buffer (image_data) that doesn't scale along the input parameters: width, height.

The fix should take care of dynamically scale and fill the buffer to correctly create the requested texture2D object