Improve layout styles sharing mechanism

As described in NXS-5205, we need to think about a better way to provide common doc type layouts styles.

Original issue is that View Designer does not generate the proper css styles for metadata layouts. It adds:

    <style>
      *[role=widget] {
        padding: 5px;
      }
    </style>

while it should have generated:

    <style>
      *[role=widget] {
        margin-bottom: 16px;
      }
      label {
        @apply --nuxeo-label;
      }
      div.multiline {
        white-space: pre-line;
      }
      div {
        word-wrap: break-word;
        overflow-wrap: break-word;
        word-break: break-word;
        -webkit-hyphens: auto;
        -moz-hyphens: auto;
        -ms-hyphens: auto;
        -o-hyphens: auto;
        hyphens: auto;
      }
    </style>

as in https://github.com/nuxeo/nuxeo-web-ui/blob/cdc1e17874787392d98dcaa02084a0e6208ca404/elements/document/file/nuxeo-file-metadata-layout.html#L26

I believe the metadata layouts needs these special CSS rules to behave well on the right-hand side of the browser.

The easy fix would be to make sure VD handles this specificity for metadata layouts (which we could maybe do for a 10.10TP fix?).
However, this is hardly maintainable as next time we'll change or add specific rules to a layout type, VD will also need adaptations.

Possible solutions/things to check:

• shouldn't we need the the metadata styles on all layouts?
• introduce some layouts common styles and add:

  <style include="nuxeo-doc-layouts-styles">
  

  to our html layouts. We could even introduce per layout type styles e.g. nuxeo-doc-metadata-layouts-styles

However, adding a layout style module will fragment styling between this module and nuxeo-styles. We will instead clean up nuxeo-styles, making the layout css rules more specific, and adding these to nuxeo-styles. See specs in TL-313. From now on, elements scaffolded on studio should now have include="nuxeo-styles" on their style block.