add allowJoinUnmutedViaIntent to the bridge

This allows us to control to never start unmuted in spa but be able to
start unmuted in widget and component mode.

component/host.test.ts

@@ -54,6 +54,21 @@ describe("useComponentHostBridge", () => {
       }),
     ).resolves.toBeUndefined();
     expect(result.current.supportsReactions).toBe(true);
+    // Starting the user unmuted unasked is something a host has to opt into
+    expect(result.current.allowJoinUnmutedViaIntent).toBe(false);
+  });
+
+  test("lets the host allow joining unmuted on the intent", () => {
+    const { result, rerender } = renderHook(
+      ({ supplied }: { supplied: ElementCallHostBridge }) =>
+        useComponentHostBridge(supplied, undefined, undefined),
+      { initialProps: { supplied: {} } },
+    );
+    expect(result.current.allowJoinUnmutedViaIntent).toBe(false);
+
+    // Read through to whatever the host most recently said
+    rerender({ supplied: { allowJoinUnmutedViaIntent: true } });
+    expect(result.current.allowJoinUnmutedViaIntent).toBe(true);
   });
 
   test("only has a close when the host has one, since that is a signal", () => {

component/host.ts

@@ -64,6 +64,14 @@ export interface ElementCallHostBridge {
    * Defaults to true.
    */
   readonly supportsReactions?: boolean;
+  /**
+   * Whether the user may start unmuted when the intent skips the lobby, so
+   * that they never see their devices before joining. Defaults to false: the
+   * user starts muted and unmutes themselves. A host that chose the intent on
+   * the user's behalf, and is sure they expect to be heard and seen at once,
+   * says so here — as a Matrix client hosting Element Call as a widget does.
+   */
+  readonly allowJoinUnmutedViaIntent?: boolean;
 }
 
 /**
@@ -164,6 +172,9 @@ export function useComponentHostBridge(
       get supportsReactions(): boolean {
         return latest.current.supportsReactions ?? true;
       },
+      get allowJoinUnmutedViaIntent(): boolean {
+        return latest.current.allowJoinUnmutedViaIntent ?? false;
+      },
       // Whatever the host says or does not say, the account is its own: it
       // signed the user in and handed us the client. So Element Call never
       // offers to edit the profile from inside a component.