IJAI-667 test the Session View terminal close-reason split

The close-reason logging landed with a spec requirement and no test, and the part
worth holding is not the wording: whether a terminated runtime's output tail is
logged at all is a decision about session content, not a formatting detail.

Extract that decision and the message it produces from the observer's private
reporting path so both can be asserted directly -- an early death carries the
tail, a longer-lived runtime carries none, and the boundary is stated once -- and
give the spec requirement its [@test] link. The unavailable-tail case now reads
like the other two instead of carrying a sentence of its own.

Restores the trailing newline TerminalViewFactory.kt lost, too.

(cherry picked from commit 84a764c6ca21a6e3c35e41249a1f74dd5d0a67a1)

GitOrigin-RevId: 2e5fce1df2a93760a000f4808f5a85072de1fed7

plugins/terminal/frontend/src/com/intellij/terminal/frontend/view/impl/TerminalViewFactory.kt

@@ -108,4 +108,4 @@ internal suspend fun TerminalView.awaitLaidOutTermSize(): TermSize? {
     TerminalUiUtils.getComponentSizeInitializedFuture(component).await()
     gridSize?.let { TermSize(it.columns, it.rows) }
   }
-}
+}