Refactor room_version support code

Fix advertising unsupported room versions

src/core/config/room_version.rs

@@ -0,0 +1,56 @@
+use ruma::{RoomVersionId, api::client::discovery::get_capabilities::v3::RoomVersionStability};
+
+use crate::Config;
+
+/// Partially supported non-compliant room versions
+pub const UNSTABLE_ROOM_VERSIONS: &[RoomVersionId] =
+	&[RoomVersionId::V2, RoomVersionId::V3, RoomVersionId::V4, RoomVersionId::V5];
+
+/// Supported and stable room versions
+pub const STABLE_ROOM_VERSIONS: &[RoomVersionId] = &[
+	RoomVersionId::V6,
+	RoomVersionId::V7,
+	RoomVersionId::V8,
+	RoomVersionId::V9,
+	RoomVersionId::V10,
+	RoomVersionId::V11,
+	RoomVersionId::V12,
+];
+
+/// Experimental and prototype room versions under development.
+pub const EXPERIMENTAL_ROOM_VERSIONS: &[RoomVersionId] = &[];
+
+impl Config {
+	#[inline]
+	#[must_use]
+	pub fn supported_room_version(&self, version: &RoomVersionId) -> bool {
+		self.supported_room_versions()
+			.any(|(supported_version, _)| &supported_version == version)
+	}
+
+	#[inline]
+	pub fn supported_room_versions(
+		&self,
+	) -> impl Iterator<Item = (RoomVersionId, RoomVersionStability)> + '_ {
+		let stable_room_versions = STABLE_ROOM_VERSIONS
+			.iter()
+			.cloned()
+			.map(|version| (version, RoomVersionStability::Stable));
+
+		let unstable_room_versions = UNSTABLE_ROOM_VERSIONS
+			.iter()
+			.filter(|_| self.allow_unstable_room_versions)
+			.cloned()
+			.map(|version| (version, RoomVersionStability::Unstable));
+
+		let experimental_room_versions = EXPERIMENTAL_ROOM_VERSIONS
+			.iter()
+			.filter(|_| self.allow_experimental_room_versions)
+			.cloned()
+			.map(|version| (version, RoomVersionStability::Unstable));
+
+		stable_room_versions
+			.chain(unstable_room_versions)
+			.chain(experimental_room_versions)
+	}
+}