Implement a QRCode payload generator

[sagar-apple]

Pulling in @bhaskar-apple's work on a QRCode Setup Payload generator

This PR includes code to generate a base45 encoded string given a setup payload.

Here is a brief description of some of the classes / functions -

1. SetupPayload - A class representing a payload that gets encoded in a QR code.
2. SetupPayloadGenerator - A class that generates a base45 encoded string given a SetupPayload object
3. SetupCodeUtils - Utility functions to encode a base45 string.

The encoding of the binary data to a base45 string is done as follows -
Every 2 bytes (16 bits) of binary source data are encoded to 3 characters of the Base-45 alphabet.
If an odd number of bytes are to be encoded, the remaining single byte is encoded to 2 characters of the Base-45 alphabet.

[sagar-apple]

@pan-apple @rwalker-apple

[sagar-apple]

This PR generates code covers stats for a bunch of headers in /usr/include, not sure why. I'm not sure if it's expected.

[sagar-apple]

Not intentional to generate code cover stats for headers in /usr/include.
My apologies if I somehow managed to do that

Haha no no don't worry :)

[rwalker-apple]

do all of our target environments support C++ static initializers?

[bhaskar-apple]

This code is the QR generation code. I would expect it to be running as a CL tool used by vendors on desktop class machines and not in the accessory themselves. So I would expect those to support it.

[sagar-apple]

Along with what Bhaskar said this might be consumed by the commissioner, so I don't necessarily see an issue there either.

[gerickson]

Devices with displays will likely also run this code. Generally, our policy with respect to OpenWeave is that C++ is fine but STL is generally prohibited unless it is strictly tooling or desktop, mobile, or server-class code only.

[bhaskar-apple]

This is meant to run only on tooling / desktop class code.
I see the use case where the device may have to show the code on a UI. But since the payload is static, I would assume the better approach is to burn the code into the device vs. having logic in the device to generate it from the payload.