Bump the minimum Android target api to 21 (Android Lollipop)

[m4gr3d]

Following the discussion below, bump the minimum Android target api to 21 (Android 5 Lollipop).

Fixes #62464
Fixes #63945

According to Google stats, raising the min supported version to Android 5 provides 98.8% device coverage.

[clayjohn]

Does this also apply when using the OpenGL renderer?

I'd be hesitant to drop support for devices that can run the OpenGL renderer still.

[m4gr3d]

Does this also apply when using the OpenGL renderer?

It shouldn't, but that would require us to provide separate template builds for Android, one with Vulkan enabled and the other without.

It's worth discussing whether we're willing to increase the build and maintenance complexity of fully disabling Vulkan in a 4.0 build.

[himaghnam]

I think Android 7 as a minimum requirements is fine, no need for a seperate build template.

[akien-mga]

It shouldn't, but that would require us to provide separate template builds for Android, one with Vulkan enabled and the other without.

We should be able to load the Vulkan library dynamically, and fallback to GLES3 if not present, no? That's the same principle for GLESv2 and GLESv3 support in 3.x.

For 3.x I think GLESv3 is provided as a stub even when not supported so we can fallback, but for Vulkan it should be even simpler as we use Volk which dlopens the Vulkan lib. If it fails initializing, we can fallback.

So unless there's very significant benefit for moving to 7.0, I would prefer not dropping ~6% of the market.

[m4gr3d]

We should be able to load the Vulkan library dynamically, and fallback to GLES3 if not present, no? That's the same principle for GLESv2 and GLESv3 support in 3.x.

According to this blog post that should be possible, though I'd like to get @BastiaanOlij take on it since he has been driving the mobile renderer implementation.

[Calinou]

I'd prefer to have the baseline on Android 6.0 – ideally 5.1, but I recognize that may be difficult. We probably don't need to support Android below 6.0 when Godot 4.0 is released, but I think there's still a fair amount of users on Android 6.0 wishing to use the OpenGL renderer.

Also, in my experience, Vulkan support is pretty broken on Android 7 and 8 anyway. The first version where it's actually usable is Android 9. If you actually set the baseline for good Vulkan support, it would be Android 9, which is too high.

[m4gr3d]

Follow-up update:

Updated the min supported version to 21 (Android 5 Lollipop). This provides 98.8% device coverage and addresses the issues reported in #62464 & #63945

[akien-mga]

Bumping to API 21 makes perfect sense for Godot 4.0. OpenGL ES 3.0 support pre-Android 5 would anyway be quite unreliable, and any Google Play release now needs to support x86_64/arm64 so API 21 is a requirement.

[akien-mga]

Thanks!