Emmet tweaks: simplify set/reset Emmet preferences and syntax profiles

[mrmlnc]

Source: #9500 and #9002

The process of set/reset preferences and syntax profiles for Emmet has been simplify. We don’t have to support undocumented features of Emmet, which don’t have any sense for the end user.

Just use Emmet API.

[coveralls]

Coverage remained the same at 60.967% when pulling f6677f1 on mrmlnc:fix-emmet-preferences-reset into 6ae0573 on Microsoft:master.

[egamma]

LGTM to thanks 🌹

[egamma]

@mrmlnc since this change this preference setting results in an error:

{
    "emmet.preferences": {
         "less.propertyEnd": "END"
     }
}

Therefore my question is less.propertyEnd a supported setting?
The implementation before this PR made sure that this property is defined in the case emmet complains:

        for (let key in preferences) {
            try {
                _emmet.preferences.set(key, preferences[key]);
            } catch (err) {
                _emmet.preferences.define(key, preferences[key]);
            }
        }

[mrmlnc]

@egamma, unfortunately, it's my mistake. I forgot about it. 😞

This PR, as specified in the description to it, removes support for undocumented features of Emmet, which don’t have any sense for the end user.

Correct code:

try {
  _emmet.loadPreferences(emmetPreferences.preferences);
  _emmet.loadProfiles(emmetPreferences.syntaxProfiles);
} catch(err) {
  // silence
}

Available settings: http://docs.emmet.io/customization/preferences/

[egamma]

@mrmlnc no problem, pushed the fix, thanks.