[engine] Replace the common libxml2 library with a pure Rust implementation

[miseyu]

Is your feature request related to a problem? Please describe.

The current version of
https://github.com/KWARC/rust-libxml
is a sys crate for libxml2 (https://github.com/GNOME/libxml2), so it may not work properly on some operating systems .

Describe the solution you'd like**

We want to create a pure rust xml crate to replace the libxml2 dependency used in https://github.com/reearth/reearth-flow/blob/main/engine/runtime/common/src/xml.rs