Invalid code generated with Java or Rust keywords as field name or ISL type name

[desaikd]

Currently, code generation can generate invalid Java or Rust code for ISL types that have names using keywords of Java/Rust programming language. This is also an issue for field names that have these keywords.

e.g.
Something like the following generates invalid rust code:

type::{
 name: bag,
 fields: closed::{
    type: {type: string, regex: "bag"},
    items: {type: shape}
 }
}

Note the field whose name is type.
This results in code like:

#[derive(Debug, Clone, Default)]
pub struct Bag {
    type: AnonymousType1,
    items: AnonymousType2,
}

For Rust, can use raw identifiers: https://doc.rust-lang.org/reference/identifiers.html#raw-identifiers
For Java, a possible solution is to add a suffix (e.g. _) for keywords used as variable/class names.

CC: @jpschorr