Implement the standard library in arr.ai

[marcelocantos]

The standard library should be a regular bit of arr.ai code. This allows simpler functions that leverage other functions to be expressed directly in arr.ai while still providing access to the builtins implement in the host language. It'll also reduce the porting effort when adding a new host language.

\native native +> (
    seq: native.seq +> (
        trim_prefix: \prefix
            let has_prefix = native.seq.has_prefix(prefix);
            \subject cond [
                has_prefix(subject): subject(prefix count:),
                *: subject,
            ],
    ),
)

[marcelocantos]

This is a blocker for #178, which is P0, so bumping to P0 as well.

[marcelocantos]

#485 and #602 will make the above example cleaner.

\native native +> (
    seq+>: (
        trim_prefix: \prefix
            let has_prefix = super.has_prefix(prefix);
            \subject cond [
                has_prefix(subject): subject(prefix count:),
                *: subject,
            ],
    ),
)