chore(UI): fullscreen use behind window blur

[BLumia]

全屏启动器直接使用背景模糊。后续会继续调整到 treeland 模糊。

Log:

[deepin-ci-robot]

deepin pr auto review

关键摘要:

• 在FullscreenFrame.qml中，background属性从Image改为Item，需要确认这是否符合设计需求。
• 在Main.qml中，新增了一个StyledBehindWindowBlur组件，需要检查其功能和样式是否符合预期。
• 在StyledBehindWindowBlur组件中，使用了blendColor属性，需要确保这个功能在所有目标平台上都表现良好。
• 在StyledBehindWindowBlur组件中，有一个条件判断if (valid)，这可能是一个潜在的错误，应该确认valid变量是否已定义。
• 在StyledBehindWindowBlur组件中，使用了DStyle.Style.control.selectColor函数，需要确保这个函数的参数和返回值符合预期。
• 在Main.qml中，新增了color: "transparent"属性，需要确认这是否符合设计要求。

是否建议立即修改:
是

[deepin-bot]

TAG Bot

New tag: 0.8.2
DISTRIBUTION: unstable
Suggest: synchronizing this PR through rebase #374

[deepin-bot]

TAG Bot

New tag: 0.8.3
DISTRIBUTION: unstable
Suggest: synchronizing this PR through rebase #384

[deepin-bot]

TAG Bot

New tag: 0.8.4
DISTRIBUTION: unstable
Suggest: synchronizing this PR through rebase #393

[deepin-bot]

TAG Bot

New tag: 0.8.5
DISTRIBUTION: unstable
Suggest: synchronizing this PR through rebase #400

[deepin-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: BLumia, justforlxz

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[deepin-bot]

TAG Bot

New tag: 0.8.6
DISTRIBUTION: unstable
Suggest: synchronizing this PR through rebase #406

[deepin-bot]

TAG Bot

New tag: 0.8.7
DISTRIBUTION: unstable
Suggest: synchronizing this PR through rebase #409

[deepin-bot]

TAG Bot

New tag: 1.0.0
DISTRIBUTION: unstable
Suggest: synchronizing this PR through rebase #413

[BLumia]

withdrew

后续仍应当使用 dtk / TreeLand 提供的糊壁纸的方案（