[Tooling] Adapt Fabulous.CodeGen to automate creation of widget builders

[TimLariviere]

In v1, we created Fabulous.CodeGen to automate the creation of wrappers around Xamarin.Forms controls.
It works by taking a mapping file (Xamarin.Forms.Core.json) which has the path to dlls and how we should map the types inside those dlls.
It outputs 2 F# files with the attribute keys and wrappers for all mapped controls.

The idea is to reuse Fabulous.CodeGen and adapt it so it can generate both Xamarin.Forms.Core.Attributes.fs and Xamarin.Forms.Core.fs

Doing this will avoid us to implement everything by hand and make a lot more controls available in v2.

[edgarfgp]

I would like to try and implement this

[edgarfgp]

After looking at the changes needed for code generation to be adapted to v2. Im not sure if will be worth as it adds a lot complexity due new way of creating and updating widgets
@TimLariviere @twop

• Xamarin.Forms.Core.json will need to be adapted to contain a new format that maps the new approach
• Xamarin.Forms.Core.json maps the Xamarin.Forms.Core API with is not going to change as the Xamarin.Forms is now out of support
• Before we had a single AttributeKey<_> and now we have : Attributes.define, Attributes.defineBindable, .. etc . Which makes the code generation(also the mapping.json) more complex
• As Already noted the are some special Widgets that we want to create like LabelStyle, ButtonStyle , FormattedLabel

IMHO I think at this stage we will get more benefit from mapping the bindable properties Xamarin.Forms.Core API manually which seems a big task but make sure we cover all the special cases .

[TimLariviere]

Closing this one in favor of #53