Although we want to ensure android-activity itself builds with the
same MSRV as Winit there's no need to also check that the examples
build with an older toolchain, and in fact in the case of Egui based
examples they don't support being built with 1.60.0.
In addition to adding an `if: rust_version == "stable"` condition
for building agdk-egui, this also adds CI stages to build agdk-mainloop,
na-mainloop and agdk-eframe to cover at least one example based on
`NativeActivity` and cover the key examples that others are most
likely to be interested in.
This reverts the changes from 66e3293f4d
to support the 1.57.0 compiler (leaving the rustdoc fixes).
Making the changes to support 1.57 felt disappointing to require for the
sake of Winit being able to better support Linux distro packaging. Even
with the changes we still wouldn't really support
1.57 without also upstreaming changes to `cargo ndk`.
The new plan is to bank on Winit bumping its own MSRV to at least
1.58 which seems more than reasonable considering that even 1.59
is already >6months old.
Ref: https://github.com/rust-windowing/winit/pull/2453
This updates ci.yml to now build with 1.60, assuming that the above
PR will be accepted.