[QuickStart] Created common logic for handling decoder errors

The goal of this change is to centralize handling decoder errors, and
express them in a common way.

With this change, Wifi Credentials parsing is now returned through
a callback with two parameters - an optional pointer to the data, and
and optional enum for an error. Future CLs will update all other
QuickStartDecoder endpoints to match this exactly.

Parsing is now done through DecodeData. DecodeData not only calls into
QuickStartDecoder, but checks the return values for sanity. If an error
code is returned, empty data is returned. If not, we
return the data through the success callback.

Future CLs will explore moving more error handling into this common method

This approach gives the following benefits:
* Less error prone error handling. Provided the decoder is only called
through this method, we can guarantee that the connection handles errors
the same regardless of what is parsed
* Simplified debugging - errors now all follow the same path, making
it way easier to figure out what happens in the error case.
* Simplified code - although some templates are used, these are commented and limited in usage.

Test: Updated Existing Tests

Bug: b/280330703
Change-Id: I52924bd152db1bb1f2980233ed71852474d972cb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4503759
Reviewed-by: Will Harris <wfh@chromium.org>
Reviewed-by: Brittany Hartmire <bhartmire@google.com>
Commit-Queue: Joe Antonetti <joeantonetti@google.com>
Reviewed-by: Michael Hansen <hansenmichael@google.com>
Cr-Commit-Position: refs/heads/main@{#1141020}