This PR includes
* Reading XML from a file, stream, or string
* Reading XML via Data.fetch
* Accessing the root element, element children, and attributes
* Accessing tag text contents
* Get tags by name
* Inner / Outer XML string
Closes#5113
Fixes a bug where read-only files would be overwritten if File.write was used in backup mode, and added tests to avoid such regression. To implement it, introduced a `is_writable` property on `File`.
- Added Encoding type
- Added `Text.bytes`, `Text.from_bytes` with Encoding support
- Renamed `File.read` to `File.read_text`
- Renamed `File.write` to `File.write_text`
- Added Encoding support to `File.read_text` and `File.write_text`
- Added warnings to invalid encodings
