egui_glow: default to RGBA8 if sRGB not supported (#2007)

The Vivante GPU on many STM32MP1 based boards does not support sRGB
as an internal format.

Introduce a check for sRGB support and default to `RGBA8` internal format
if not supported.

Additionally the STM32MP1 needs to be checked for `GL_ARB_vertex_array_object`

Closes #1991

crates/egui_glow/src/vao.rs

@@ -147,6 +147,7 @@ fn supports_vao(gl: &glow::Context) -> bool {
             let supported_extensions = gl.supported_extensions();
             tracing::debug!("Supported OpenGL extensions: {:?}", supported_extensions);
             supported_extensions.contains("ARB_vertex_array_object")
+                || supported_extensions.contains("GL_ARB_vertex_array_object")
         } else {
             true
         }