Layout Builder sections are now keyed by UUID and ordered by weight

To allow for predictability in config comparison operations, UUID and weight properties have been added to the Layout Builder sections.

Before:

third_party_settings:
  layout_builder:
    allow_custom: true
    enabled: true
    sections:
      -
        layout_id: onecol
        layout_settings:
          label: Section 10
        components:
          b2b52d3d-749f-4ef4-a4f0-dd187ea3a10e:
            uuid: b2b52d3d-749f-4ef4-a4f0-dd187ea3a10e
            region: body
            configuration:
              id: some_block
              label: 'Some Block'
              provider: some_provider
              label_display: '0'
              context_mapping: {  }
            additional: {  }
            weight: 0
        third_party_settings: {  }

After:

third_party_settings:
  layout_builder:
    allow_custom: true
    enabled: true
    sections:
      364e88fc-e764-43c8-8273-e89fe355d6d4:
        uuid: 364e88fc-e764-43c8-8273-e89fe355d6d4
        layout_id: onecol
        layout_settings:
          label: Section 10
        components:
          b2b52d3d-749f-4ef4-a4f0-dd187ea3a10e:
            uuid: b2b52d3d-749f-4ef4-a4f0-dd187ea3a10e
            region: body
            configuration:
              id: some_block
              label: 'Some Block'
              provider: some_provider
              label_display: '0'
              context_mapping: {  }
            additional: {  }
            weight: 0
        weight: 0
        third_party_settings: {  }

\Drupal\layout_builder\SectionListTrait::removeSection() accepts UUID instead of delta as an argument.
Example: $this->sectionList->removeSection('11000000-0000-1000-a000-000000000000');