feat(windows): keep dwm shadow on frameless windows

[chen-zeong]

Fixes #13134.

Summary

• keep the native DWM shadow when Windows decorations are disabled so frameless windows stay resizable
• store the shadow preference on WindowWrapper and drive it from SetShadow/SetDecorations handlers
• add a dedicated shadow helper to toggle and reset DWM attributes

Testing

• set decorations: false and shadow: true in examples/helloworld/tauri.conf.json
• cargo run --example helloworld (Windows 10) and verify the window stays frameless, keeps its shadow, and remains resizable from every edge

[github-actions]

Package Changes Through b5cefdc

There are 10 changes which include @tauri-apps/api with minor, tauri-cli with minor, tauri-utils with minor, tauri-runtime-wry with minor, tauri-runtime with minor, tauri with minor, tauri-bundler with minor, @tauri-apps/cli with minor, tauri-codegen with patch, tauri-macros with patch

Planned Package Versions

The following package releases are the planned based on the context of changes in this pull request.

package	current	next
@tauri-apps/api	2.8.0	2.9.0
tauri-utils	2.7.0	2.8.0
tauri-bundler	2.6.1	2.7.0
tauri-runtime	2.8.0	2.9.0
tauri-runtime-wry	2.8.1	2.9.0
tauri-codegen	2.4.0	2.4.1
tauri-macros	2.4.0	2.4.1
tauri-plugin	2.4.0	2.4.1
tauri-build	2.4.1	2.4.2
tauri	2.8.5	2.9.0
@tauri-apps/cli	2.8.4	2.9.0
tauri-cli	2.8.4	2.9.0

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[Think-M]

@FabianLars Does this provide a good solution? : )

[Think-M]

@chen-zeong Brother, can you continue to handle this issue? I urgently need it here. Thank you for your contribution!

[chen-zeong]

@chen-zeong Brother, can you continue to handle this issue? I urgently need it here. Thank you for your contribution!

this solution isn't perfect, but it does work.

When it launches, you'll see a border, but it's gone in like half a second.

I've looked at all the popular Tauri projects, and on Windows 10, they all have those unacceptable triple borders because they're trying to use a custom title bar.

Right now, I'm using a modified Tauri version for both of my apps.

You can just look at my forked branch and use it locally.

[Think-M]

@chen-zeong Brother, can you continue to handle this issue? I urgently need it here. Thank you for your contribution!

this solution isn't perfect, but it does work.

When it launches, you'll see a border, but it's gone in like half a second.

I've looked at all the popular Tauri projects, and on Windows 10, they all have those unacceptable triple borders because they're trying to use a custom title bar.

Right now, I'm using a modified Tauri version for both of my apps.

You can just look at my forked branch and use it locally.

It's already quite good to achieve such an effect, at least much better than the border that has always existed before.

I strongly recommend merging it into the official version, which may require you to push it forward further.

Half a second is not a big problem at all. I think users can bypass it by delaying the display window by half a second. Anyway, this turns a big problem that cannot be bypassed into a small problem that can be bypassed.