File: Re-add support to skip CR (`\r`) in `File::get_as_text`
This was removed in #63481, and we confirmed that it's better like this,
but we add back the possibility to strip CR as an option, to optionally
restore the previous behavior.
For performance this is done directly in `String::parse_utf8`.
Also fixes Android `FileAccess::get_line()` as this one _should_ strip CR.
Supersedes #63717.
+ Returns the whole file as a [String]. Text is interpreted as being UTF-8 encoded.
+ If [code]skip_cr[/code] is [code]true[/code], carriage return characters ([code]\r[/code], CR) will be ignored when parsing the UTF-8, so that only line feed characters ([code]\n[/code], LF) represent a new line (Unix convention).