Add required features to manifest for shader_material_glsl example

[rparrett]

Objective

Fixed #8505

Solution

Add required-features to the cargo manifest for that example.

There's precedent for this with the tonemapping example which requires non-default features ktx2 and zstd.

Now when running the example, you see a friendly error message:

 cargo run --example shader_material_glsl
error: target `shader_material_glsl` in package `bevy` requires the features: `shader_format_glsl`
Consider enabling them by passing, e.g., `--features="shader_format_glsl"`

[mockersf]

There's precedent for this with the tonemapping example which requires non-default features ktx2 and zstd.

Those two features are actually part of the default set and should be removed from the required-features of that example.

I would prefer the example to check that the feature is enabled before calling the code requiring the features than adding that

[rparrett]

I would prefer the example to check that the feature is enabled before calling the code requiring the features than adding that

Could you explain that preference a bit more? Is required-features only meant to be used when a feature is required for compilation? Is that distinction useful in this case?

It's handy to have that metadata available for prototype_bevy_example_runner.

[mockersf]

Could you explain that preference a bit more? Is required-features only meant to be used when a feature is required for compilation? Is that distinction useful in this case?

Thinking about this more, it doesn't really fly...

What do you think of either:

• removing that example. This means we consider glsl support something that we don't want to promote that much
• adding feature shader_format_glsl to the default features of Bevy. This was the case before make glsl and spirv support optional #8491

It's handy to have that metadata available for prototype_bevy_example_runner.

In my experience building all the examples, it's best (for total build time) to use the same set of feature for all and not change per example.

[rparrett]

Closing in favor of #8969