vulkan: correctly set INDEPENDENT_BLEND，make runable on Android 8.x

[jinleili]

Connections
#2419

Description
Andorid 8.x(Vulkan 1.0) doesn't support the independent_blend feature, running on these devices failed at request_device :
W/wgpu_hal::vulkan: Unrecognized device error ERROR_FEATURE_NOT_PRESENT

Testing
Tested on these devices:
Samsung Galaxy S7 edge (Android 8.0)
Google Nexus 5x (Android 8.1)
OPPO R15 (Android 8.1)
HuaWei MatePad 11 (Android 10)
Google Pixel 5 (Android 12)
via wgpu-on-app.

Pixel 5 successfully runs all examples before and after this commit.

On MatePad 11, only HDR ASTC example keeps failing because the TEXTURE_COMPRESSION_ASTC_HDR feature is not supported.

The boid, masa-line, and cube examples previously only runs on Pixel 5 and MatePad 11, and successfully runs on all devices now.

water and shadow examples failed on Galaxy S7 edge and Nexus 5x that because of naga compiling shader error, also tried updating naga to latest commit and got the same result:
shadow error:

2022-02-22 14:48:46.857 9101-9101/name.jinleili.wgpu I/naga::back::spv::writer: Skip function Some("fetch_shadow")
2022-02-22 14:48:46.864 9101-9101/name.jinleili.wgpu I/Adreno: Shader compilation failed for shaderType: 1
2022-02-22 14:48:46.864 9101-9101/name.jinleili.wgpu W/wgpu_hal::vulkan: Unrecognized device error INCOMPLETE
2022-02-22 14:48:46.864 9101-9101/name.jinleili.wgpu E/wgpu::backend::direct: Handling wgpu errors as fatal by default

water error:

2022-02-22 14:51:02.403 9465-9465/name.jinleili.wgpu D/naga::valid::function: var LocalVariable { name: Some("out"), ty: [7], init: None }
2022-02-22 14:51:02.514 9465-9465/name.jinleili.wgpu I/Adreno: Shader compilation failed for shaderType: 1
2022-02-22 14:51:02.514 9465-9465/name.jinleili.wgpu W/wgpu_hal::vulkan: Unrecognized device error INCOMPLETE
2022-02-22 14:51:02.514 9465-9465/name.jinleili.wgpu E/wgpu::backend::direct: Handling wgpu errors as fatal by default

water example running on OPPO R15 get weird render result:

[kvark]

very nice!
I added this to https://github.com/gfx-rs/wgpu/wiki/Vulkan-Requirements