Migrate to MSAL 1.2.0

[bawoodruff]

This commit addresses incompatibilities in the current msal-flutter due to changes in the underlying MSAL components.

[mswehli]

hey @bawoodruff, thanks so much for submitting this. Just need a few days to look over it, but would you be able to change the version number to 1.2.0, just as i'm trying to keep the version numbers inline with the official MSAL library version numbers. Find it easier to help you know which version of the library you'll be getting since it's a wrapper.

[bawoodruff]

@mswehli - checking in on this pull request, I'd like to use a published version of the plugin,. Are you still using the MSAL library?

[mswehli]

@bawoodruff Sorry about the delay, but before i can merge it I have to make sure of how the 1.2.0 libraries are implemented, as requiring a redirect url is a breaking change and departs from the original behaviour of a platform specific default redirect url. So I would need more time to test the platform native libraries to see how they behave. I'm a little busy with some client work at the moment but have set aside some time at the end of the week to go over it in more detail.