feat(android): open share links from a browser or the share sheet

A drive.proton.me/urls/ link opened from a browser, or text containing
one shared to the app, switches to Shares and opens the Add form with
the link filled in, fragment included. A playing episode moves to the
mini transport instead of covering the form. A recreated activity does
not offer the same link again.

The view filter is not autoVerify, since the domain is Proton's, so
Android only routes browser links here once "Open supported links" is
allowed in the app's settings; sharing works without that.

android/app/src/test/java/io/narl/protonstream/IncomingShareLinkTest.kt

@@ -0,0 +1,37 @@
+package io.narl.protonstream
+
+import android.content.Intent
+import org.junit.Assert.assertEquals
+import org.junit.Assert.assertNull
+import org.junit.Test
+
+class IncomingShareLinkTest {
+    private val link = "https://drive.proton.me/urls/ABC123#s3cr3t"
+
+    @Test
+    fun `a viewed share link is taken whole, fragment included`() {
+        assertEquals(link, shareLinkFrom(Intent.ACTION_VIEW, link, null))
+    }
+
+    @Test
+    fun `a viewed url that is not an https share link is ignored`() {
+        assertNull(shareLinkFrom(Intent.ACTION_VIEW, "https://drive.proton.me/u/0/", null))
+        assertNull(shareLinkFrom(Intent.ACTION_VIEW, "http://drive.proton.me/urls/ABC123#s3cr3t", null))
+    }
+
+    @Test
+    fun `a shared message yields the link inside it`() {
+        assertEquals(link, shareLinkFrom(Intent.ACTION_SEND, null, "Season two is up: $link enjoy"))
+        assertEquals(link, shareLinkFrom(Intent.ACTION_SEND, null, "(<$link>)"))
+    }
+
+    @Test
+    fun `a shared message without a link yields nothing`() {
+        assertNull(shareLinkFrom(Intent.ACTION_SEND, null, "no link here"))
+    }
+
+    @Test
+    fun `other actions are ignored`() {
+        assertNull(shareLinkFrom(Intent.ACTION_MAIN, link, link))
+    }
+}