encode/decode for multiple alphabets (#13428)

Based on the discussion in #13419.


## Description

Reworks the `decode`/`encode` commands by adding/changing the following
bases:

- `base32`
- `base32hex`
- `hex`
- `new-base64`

The `hex` base is compatible with the previous version of `hex` out of
the box (it only adds more flags). `base64` isn't, so the PR adds a new
version and deprecates the old one.

All commands have `string -> binary` signature for decoding and `string
| binary -> string` signature for encoding. A few `base64` encodings,
which are not a part of the
[RFC4648](https://datatracker.ietf.org/doc/html/rfc4648#section-6), have
been dropped.


## Example usage

```Nushell
~/fork/nushell> "string" | encode base32 | decode base32 | decode
string
```

```Nushell
~/fork/nushell> "ORSXG5A=" | decode base32
# `decode` always returns a binary value
Length: 4 (0x4) bytes | printable whitespace ascii_other non_ascii
00000000:   74 65 73 74                                          test
```


## User-Facing Changes

- New commands: `encode/decode base32/base32hex`.
- `encode hex` gets a `--lower` flag.
- `encode/decode base64` deprecated in favor of `encode/decode
new-base64`.

crates/nu-command/src/default_context.rs

@@ -179,8 +179,16 @@ pub fn add_shell_command_context(mut engine_state: EngineState) -> EngineState {
             Char,
             Decode,
             Encode,
+            DecodeHex,
+            EncodeHex,
+            DecodeBase32,
+            EncodeBase32,
+            DecodeBase32Hex,
+            EncodeBase32Hex,
             DecodeBase64,
             EncodeBase64,
+            DecodeBase64Old,
+            EncodeBase64Old,
             DetectColumns,
             Parse,
             Split,