Fix duplicated "Internal shared storage" when opening MTP device from sidebar

Issue:
When opening an MTP device via the sidebar, Dolphin shows one "Internal shared storage" folder. However, clicking the entry again results in a duplicate folder being displayed. This regression was introduced by !865 (merged) (commit 6c7c0471).

Reason:
The URL of an MTP device in the sidebar is mtp:udi=/org/kde/solid/udev/sys/devices/.... When clicking to open the MTP device, it is redirected to mtp:/....

• On the first click (no cache), KCoreDirListerCache::slotUpdateResult() calls KCoreDirListerPrivate::emitItems().
• On the second click (with cache), KCoreDirListerCache::slotRedirection() first calls KCoreDirListerPrivate::emitItems().
  Besides, DolphinTabPage::slotViewUrlRedirection() calls KCoreDirLister::openUrl(), which triggers CachedItemsJob::start(), and eventually calls KCoreDirListerPrivate::emitItems() again.
  As a result, two KCoreDirLister::itemsAdded signals are emitted, causing m_pendingItemsToInsert to be appended twice.

Change:
Add optional reload parameter to DolphinView::setUrl() and use it on URL redirection.

BUG: 506634
CCBUG: 497313