feat: [Customize menu] Customize menu merging

[pppanghu77]

Merge menus with the same name

Log: [Customize menu] Customize menu merging
Task: https://pms.uniontech.com/task-view-363005.html

[deepin-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: Johnson-zs, pppanghu77

The full list of commands accepted by this bot can be found here.

Needs approval from an approver in each of these files:

• debian/deepin/OWNERS

Approvers can indicate their approval by writing /approve in a comment
Approvers can cancel approval by writing /approve cancel in a comment

[deepin-ci-robot]

deepin pr auto review

关键摘要:

• 在isExist变量赋值后没有使用else语句，可能导致isExist始终为false。
• for (QAction *subaction : action->menu()->actions())循环中没有检查subaction是否为nullptr，可能会导致空指针解引用。
• existAction->menu()->addAction(subaction)调用可能需要检查existAction->menu()是否为nullptr。
• d->cacheActionsSeparator.insert(action, actionData.separator())调用可能需要检查actionData.separator()是否为有效的分隔符值。
• actionData.separator()的定义未在代码片段中显示，需要确认其有效值范围。

是否建议立即修改:
是

[pppanghu77]

/merge