Fix the focus issue of SmartTag/DropDown by preserving the modal menu tracking of ToolStripDropDown.

[LeafShi1]

Fixes #14600

Root Cause

PR #14491 tightened ToolStrip focus handling to avoid accidental menu activation for normal tab navigation.
The new logic worked for regular ToolStrip, but it also affected ToolStripDropDown scenarios (including SmartTag-hosted UI):

1. On focus transitions, modal menu tracking was gated too aggressively.
2. On kill-focus, active ToolStrip/menu mode could be cleared too early for drop-down hosts.
3. Once menu mode exited prematurely, the expected auto-dismiss behavior on subsequent UI navigation (such as tab switching) could break.

Proposed changes

• Keep the [Accessibility] ToolStrip (TabStop=true) intercepts arrow keys after tab navigation, preventing TreeView from handling them (.NET 10 regression) #14489 fix for regular ToolStrip focus behavior.
• Restore ToolStripDropDown focus/menu tracking behavior to avoid premature menu-mode exit.
• Update ToolStrip focus handling in WM_SETFOCUS/WM_KILLFOCUS to treat DropDown and non-DropDown separately.

Customer Impact

• The SmartTag dialog can be exited normally when switch the TabPage items

Regression?

• Yes

Risk

• Minimal

Screenshots

Before

The SmartTag dialog doesn't disappear when switch the Tabpage items

Actual11.mp4

After

The SmartTag can be closed normally when switching the TabPage items

AfterChanges.mp4

Test methodology

• Manualy

Test environment(s)

• .net 11.0.0-preview.5.26258.110

Microsoft Reviewers: Open in CodeFlow

[SimonZhao888]

Looks good to me!