This is mostly to ease setup and configuration with sandboxed browsers.
The socket currently existing in `$XDG_RUNTIME_DIR`. When sandboxing a browser, it would be unsafe to mount this directory inside the sandbox.
Mounting the socket into the sandbox's filesystem is also not possible in cases where KeePassXC is [re]started after the browser has started.
This commit moves the socket into its own isolated subdirectory, which can be safely mounted into sandboxes. Sandbox engines can create the directory themselves (in case the browser starts before KeePassXC). Both Flatpak and Firejail support this configuration.
A symlink is also created, linking the previous location to the new location. This is meant for backwards compatibility and should eventually be dropped.
The directory can't be named `org.keepassxc.KeePassXC.BrowserServer`,
since that would collide with the symlink. Instead, the directory has been created to match the format used for Flatpak builds, which make it a bit less of a snowflake build, while following accepted conventions.
Given that the preferred path now matches what Flatpak uses, the block handling Flatpak and non-Flatpak is now the same.
If `$XDG_RUNTIME_DIR` is undefined, the temporary directory is used, though reading the socket from this location is discouraged.
Closes: https://github.com/keepassxreboot/keepassxc/issues/8018
References: https://github.com/keepassxreboot/keepassxc/discussions/6741
* Removed option to attach KeePassXC to the browser extension. Users must use the proxy application to communicate with KeePassXC.
* Significantly streamlined proxy code. Used same implementation of stdin/stdout interface across all platforms.
* Moved browser service entry point to BrowserService class instead of NativeMessagingHost. BrowserService now coordinates the communication to/from clients.
* Moved settings page definition out of MainWindow
* Decoupled BrowserService from DatabaseTabWidget
* Reduced complexity of various functions and cleaned the ABI (public vs private).
* Eliminated BrowserClients class, moved functionality into the BrowserService
* Renamed HostInstaller to NativeMessageInstaller and renamed NativeMessageHost to BrowserHost.
* Recognize XDG_CONFIG_HOME when installing native message file on Linux. Fix#4121 and fix#4123.
