Create two new data structures in the `script` crate to hold senders and
receiver:
- `ScriptThreadSenders`: holds all outgoing channels from the
`ScriptThread` including a channel to the `ScriptThread` itself. The
ultimate goal with this is to reduce duplication by giving a boxed
version of this this to `Window`s.
- `ScriptThradReceivers`: holds all incoming channels to the
`ScriptThread`. This isn't cloenable like the senders. This is used to
abstract away `recv()` and `try_recv()` methods used to make the
`ScriptThread` event loop easier to read.
In addition:
- The many duplicated `ScriptThread` self-senders for the `TaskManager`
have been removed and, in general, a lot of boilerplate is removed as
well.
- Visibilty of all methods affected by this change is changed to
`pub(crate)` in order to take advantage of dead code detection. Some
dead code produced from macros is removed.
- Some conversion code is refactord into implementations of the `From`
trait.
- The names of channels uses a standard "sender" and "receiver" naming
as well as trying to be descriptive of where they go in `ScriptThread`
as well as `InitialScriptState`
Signed-off-by: Martin Robinson <mrobinson@igalia.com>
