[Feature Request] Add `endianness` to `TargetInfo`

[lsh]

Review Mojo's priorities

• [X] I have read the roadmap and priorities and I believe this request falls within the priorities.

What is your request?

I believe getting the endianness of a target is useful for working with binary data and the like.
This method could look something like:

struct Endianness:
    alias little = 0
    alias big = 1

# in TargetInfo
fn endianness() -> Endianness:

### What is your motivation for this change?

```shell
Knowing if a target wants little or big endian is useful when working with binary data.

Any other details?

No response

[abduld]

Sounds like a great suggestion and is simple to implement. Thanks