Add option for default reply privacy set to unlisted by default (#4496)

This PR fixes https://github.com/tuskyapp/Tusky/issues/2798 and is
mostly based on and supersedes
https://github.com/tuskyapp/Tusky/pull/2826 but I have fixed all merge
conflicts and unit tests.

I tested the changes locally and the setting takes effect immediately
for replies, and persists across killing the app.

---------

Co-authored-by: Eva Tatarka <eva@tatarka.me>
Co-authored-by: Konrad Pozniak <connyduck@users.noreply.github.com>

app/src/test/java/com/keylesspalace/tusky/components/compose/ComposeViewModelTest.kt

@@ -0,0 +1,65 @@
+package com.keylesspalace.tusky.components.compose
+
+import androidx.test.ext.junit.runners.AndroidJUnit4
+import com.keylesspalace.tusky.appstore.EventHub
+import com.keylesspalace.tusky.db.AccountManager
+import com.keylesspalace.tusky.db.entity.AccountEntity
+import com.keylesspalace.tusky.entity.Status
+import com.keylesspalace.tusky.network.MastodonApi
+import org.junit.Assert.assertEquals
+import org.junit.Before
+import org.junit.Test
+import org.junit.runner.RunWith
+import org.mockito.kotlin.doReturn
+import org.mockito.kotlin.mock
+import org.robolectric.annotation.Config
+
+@Config(sdk = [28])
+@RunWith(AndroidJUnit4::class)
+class ComposeViewModelTest {
+
+    private lateinit var api: MastodonApi
+    private lateinit var accountManager: AccountManager
+    private lateinit var eventHub: EventHub
+    private lateinit var viewModel: ComposeViewModel
+
+    @Before
+    fun setup() {
+        api = mock()
+        accountManager = mock {
+            on { activeAccount } doReturn
+                AccountEntity(
+                    id = 1,
+                    domain = "test.domain",
+                    accessToken = "fakeToken",
+                    clientId = "fakeId",
+                    clientSecret = "fakeSecret",
+                    isActive = true
+                )
+        }
+        eventHub = EventHub()
+
+        viewModel = ComposeViewModel(
+            api = api,
+            accountManager = accountManager,
+            mediaUploader = mock(),
+            serviceClient = mock(),
+            draftHelper = mock(),
+            instanceInfoRepo = mock(),
+        )
+    }
+
+    @Test
+    fun `startingVisibility initially set to defaultPostPrivacy for post`() {
+        viewModel.setup(null)
+
+        assertEquals(Status.Visibility.PUBLIC, viewModel.statusVisibility.value)
+    }
+
+    @Test
+    fun `startingVisibility initially set to replyPostPrivacy for reply`() {
+        viewModel.setup(ComposeActivity.ComposeOptions(inReplyToId = "123"))
+
+        assertEquals(Status.Visibility.UNLISTED, viewModel.statusVisibility.value)
+    }
+}