Add check_is_channel_participant

Refactor permission checks to load ancestor permissions into memory
for all checks to make the different logics more explicit.

crates/collab/src/tests/channel_tests.rs

@@ -6,7 +6,10 @@ use call::ActiveCall;
 use channel::{ChannelId, ChannelMembership, ChannelStore};
 use client::User;
 use gpui::{executor::Deterministic, ModelHandle, TestAppContext};
-use rpc::{proto, RECEIVE_TIMEOUT};
+use rpc::{
+    proto::{self},
+    RECEIVE_TIMEOUT,
+};
 use std::sync::Arc;
 
 #[gpui::test]