fix: example_emscripten_wgpu WGPUInstance failed to be created

[smileorigin]

The current example_emscripten_wgpu demo cannot run properly and will have the following errors:

The way to fix it is to use wgpuCreateInstance(nullptr) to create wgpu::Surface, and also add the logic to obtain the best format for the current browser（Surface:: GetPreferredFormat()）.

[ocornut]

Hello,
Thanks for the PR. Seems like this is aimed to solve #6640.

and also add the logic to obtain the best format for the current browser（Surface:: GetPreferredFormat()）

Can you clarify this? as I understand, it is unrelated to the first change? It is required? (asking for future reference)

[smileorigin]

Hello, Thanks for the PR. Seems like this is aimed to solve #6640.

and also add the logic to obtain the best format for the current browser（Surface:: GetPreferredFormat()）

Can you clarify this? as I understand, it is unrelated to the first change? It is required? (asking for future reference)

Yes, in order to resolve #6640

and also add the logic to obtain the best format for the current browser（Surface:: GetPreferredFormat()）

This is not necessary, just to resolve the warning in the browser.
By using GetPreferredFormat(), we can obtain the best format supported by the browser for optimal performance.

If you feel that the content is not related to the PR label, I can also split it into two PRs for submission.

[ocornut]

If you feel that the content is not related to the PR label, I can also split it into two PRs for submission.

It's ok. My worry is that preferred browser format might be incompatible with some of our needs, but I guess we'll find out.

Merged as 981abb4. Thank you!