feat: add attributes for drag region

[BillGoldenWater]

What kind of change does this PR introduce?

• Bugfix
• Feature
• Docs
• New Binding issue #___
• Code style update
• Refactor
• Build-related changes
• Other, please describe:

Does this PR introduce a breaking change?

• Yes, and the changes were approved in issue #___
• No

Checklist

• When resolving issues, they are referenced in the PR's title (e.g fix: remove a typo, closes #___, #___)
• A change file is added if any packages will require a version bump due to this PR per the instructions in the readme.
• I have added a convincing reason for adding this feature, if necessary

Other information

It's useful for set a element that has many children draggable.

eg.

A floating window need to be draggable when drag on any where, and can toggle maximize on double click on title.

Use to need set data-tauri-drag-region everywhere, and need to manually implement it for region that doesn't need maximize.

This PR let developer could achieve this just by set body attributes to data-tauri-drag-region-container and title container to data-tauri-drag-region-container data-tauri-drag-region-titlebar.

Description:

data-tauri-drag-region: mark this element as "drag region"

data-tauri-drag-region-container: children are also considered drag regions

data-tauri-drag-region-titlebar: the "drag region" maximizes window on double click (default when only data-tauri-drag-region is used)

data-tauri-drag-region-exclude: this element doesn't trigger drag

Example:

<div class="titlebar"
     data-tauri-drag-region-container="true"
     data-tauri-drag-region-titlebar="true"
>
  <div>Title</div>
  <div>Some decoration</div>
  <button data-tauri-drag-region-exclude>close</button>
</div>

[amrbashir]

Could you give some examples on how these might interact with each other? specifically the new ones.

[amrbashir]

one more question does data-tauri-drag-region-container require data-tauri-drag-region to be also set or do they work independently? I think they should be independent from each other and if they are both present data-tauri-drag-region would take the precedence and disable all other attributes (i.e. use the old behavior)

[lucasfernog]

I think we should target this to v2 so it also has some time to be tested by everyone while it's unstable.