Use JVM default file encoding as fallback

[balajirrao]

When the Shell is run with a file with .js extension, the content-type is determined to be text/javascript, which leads to the 8859_1 encoding to be used. AFAICT this is obsolete now. Change it to use the JVM default encoding.

[aardvark179]

I'm not sure about this. Prior to OpenJDK 18 the default character set is not necessarily a great choice. It might be worth picking UTF-8 explicitly for consistency. Have a look at JEP 400, especially:

In JDK 17 and earlier, the default charset is determined when the Java runtime starts. On macOS, it is UTF-8 except in the POSIX C locale. On other operating systems, it depends upon the user's locale and the default encoding, e.g., on Windows, it is a codepage-based charset such as windows-1252 or windows-31j.

[balajirrao]

I'm not sure about this. Prior to OpenJDK 18 the default character set is not necessarily a great choice. It might be worth picking UTF-8 explicitly for consistency. Have a look at JEP 400, especially:

@aardvark179 Yeah, I wasn't too sure about it either. Your suggestion sounds reasonable; prior to OpenJDK 18, it wasn't configurable either (according to JEP 400).