implement Display trait for most error types

[bbogdan-ov]

This simple PR adds human readable Display implementation for most error types to simplify error handling

Namely for these types:

• ShaderError
• ShaderType
• EglError
• X11Error
• Error in src/fs.rs
• Error in src/native/module.rs

Error handling example:

let conf = miniquad::conf::Conf::default();

// `MyWindow::new()` returns `Result<MyWindow, ShaderError>`
miniquad::start(conf, move || match MyWindow::new() {
    Ok(window) => Box::new(window),
    Err(e) => {
        eprintln!("Miniquad error: {e}");
        std::process::exit(1);
    }
});

#version 330

layout (location = 0) in vec2 in_pos;
layout (location = 1) in vec2 in_uv;

out vec2 uv;

void main() {
    uv = in_uv;
    I_MISSPELLED_VAR_NAME = vec4(in_pos, 0.0, 1.0);
}

Error message before:

Miniquad error: CompilationError { shader_type: Vertex, error_message: "0:10(2): error: `I_MISSPELLED_VAR_NAME' undeclared\n0:10(2): error: value of type vec4 cannot be assigned to variable of type error" }

After:

Miniquad error: Vertex shader error:
0:10(2): error: `I_MISSPELLED_VAR_NAME' undeclared
0:10(2): error: value of type vec4 cannot be assigned to variable of type error

EDIT: updated examples for more context

[not-fl3]

Thanks for PR!