Consider merging package.json and snap.manifest.json

[ritave]

Having more files to manage per Snap is more confusing for the user. I don't see why should we separate package.json and snap.manifest.json when Visual Studio Code extensions have been doing just fine with one file as a manifest.

I suggest we follow suit and merge the files

[rekmarks]

We decided to separate the snap manifest from package.json so that we are (1) not bound by its conventions when snaps are allowed to be published outside of the npm ecosystem and (2) able to dictate our manifest format without concern for compliance with third party standards. In addition, adding a bunch of fields to package.json can make it very difficult to read (3).

If someone produces a draft specification that merges the existing one with package.json that allays these concerns, we can of course entertain it.

[FrederikBolding]

We decided not to do this.