feat(core): expose invoke key for custom IPC implementations

[lucasfernog]

custom IPC systems that manually call Webview::on_message must know the invoke key checked by Tauri. This exposes that key in the App/AppHandle instances.

This is safe because the key is never leaked to remote denied webview URLs

[github-actions]

Package Changes Through abe190a

There are 5 changes which include @tauri-apps/api with patch, tauri with patch, tauri-bundler with patch, tauri-cli with patch, @tauri-apps/cli 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	2.0.1	2.0.2
tauri-bundler	2.0.1	2.0.2
tauri	2.0.1	2.0.2
@tauri-apps/cli	2.0.1	2.0.2
tauri-cli	2.0.1	2.0.2

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