Fix fragments that update other profiles

[lhecker]

SettingsLoader::_parse used to skip profiles which didn't have either a "guid"
or "name" field, due to #9962. This is however wrong for fragment loading, as
fragments can alternatively use an "updates" field instead of guid/name.

SettingsLoader::_parse was updated to allow profiles with this alternative
field during fragment loading.

PR Checklist

• Closes Fragments that update profiles don't work #11331
• I work here
• Tests added/passed

Validation Steps Performed

• Wrote the following to
  %LOCALAPPDATA%\Microsoft\Windows Terminal\Fragments\test\test.json:

  {
    "profiles": [
      {
        "updates": "{574e775e-4f2a-5b96-ac1e-a2962a402336}",
        "background": "#FFD700"
      }
    ]
  }

[lhecker]

Use white-space suppression to review 👌: https://github.com/microsoft/terminal/pull/11343/files?diff=split&w=1

[zadjii-msft]

@msftbot make sure @PankajBhojwani signs off on this

[ghost]

Hello @zadjii-msft!

Because you've given me some instructions on how to help merge this pull request, I'll be modifying my merge approach. Here's how I understand your requirements for merging this pull request:

• I'll only merge this pull request if it's approved by @PankajBhojwani

If this doesn't seem right to you, you can tell me to cancel these instructions and use the auto-merge policy that has been configured for this repository. Try telling me "forget everything I just told you".

[lhecker]

@msftbot merge this in 2 minutes

[ghost]

Hello @lhecker!

Because you've given me some instructions on how to help merge this pull request, I'll be modifying my merge approach. Here's how I understand your requirements for merging this pull request:

• I'll only merge this pull request if it's approved by @PankajBhojwani
• I won't merge this pull request until after the UTC date Mon, 27 Sep 2021 17:09:02 GMT, which is in 2 minutes

If this doesn't seem right to you, you can tell me to cancel these instructions and use the auto-merge policy that has been configured for this repository. Try telling me "forget everything I just told you".