This was a regression following the move to the edition 2021.
The CallbackUserData was not capture in the lamda, its member were moved.
So the destructor was called right after it was set.
We must make sure we capture the whole CallbackUserData, so put the callback
inside of it. This also reduce a bit of code duplication at the same time.
Test the callback invokation with statefull lambda
We want to be able to put existing functionality behind a feature flag while keeping
the semver compatibility.
This is only possible if that new feature flag is enabled by default, but this is not
working if the users have done `default-features = false` in their Cargo.toml.
So we add new `compat-x-y-z` feature that is mandatory to have and which is
enforced with a `compile_error!`
Now, users that whishes to not have the default features must enable it explicitly.
Say we want only x11 but not qt and wayland, the user will do
```toml
sixtyfps = { version = "0.2", default-features = false, features = ["x11", "compat-0-2-0"] }
```
Now, imagine that in the version 0.2.3, we put the SVG support behind a feature flag.
we will do this in out Cargo.toml:
```toml
[features]
default = ["compat-0-2-0", "x11", "wayland"]
compat-0-2-0 = ["compat-0-2-3", "svg"]
compat-0-2-3 = []
svg = [...]
...
```
That way, the svg feature will be enabled by default for all the users who used previous version
of SixtyFPS, and people that want to disable "svg" can just change from compat-0-2-0 to
compat-0-2-3 in their Cargo.toml
Move "internal" crates into the `internal` directory. This first batch
includes most of sixtyfps_runtime but leaves the rendering backends
alone for now.
pre-commit applied some cleanups to the moved files:
- Consistent newline at end of file policy
- trimming trailing whitespace
- Formatting Cargo.toml files.
