EssentialProperties: allow schemeIdUri+value pairs

[stschr]

To follow up on #4384 and enhance #4385

We think it's a good idea to enable setting pairs of @schemeIdUri + values as known essentialProperties.

To enable this, I have two options available:

1. add a second item supportedEssentialPropertySchemeValues to Settings.js;

capabilities: {
    filterUnsupportedEssentialProperties: true,
    supportedEssentialProperties: [Constants.FONT_DOWNLOAD_DVB_SCHEME, ...Constants.THUMBNAILS_SCHEME_ID_URIS],
    supportedEssentialPropertySchemeValues: [...Constants.SCHEME_ID_URI_SDR],
    useMediaCapabilitiesApi: false
},

with (in Constants.js)

SCHEME_ID_URI_SDR: [
        {schemeIdUri: 'urn:mpeg:mpegB:cicp:ColourPrimaries', value: '5'}
],

2. enhance supportedEssentialProperties with @value which can utilize RegEx, similar to this:

capabilities: {
    filterUnsupportedEssentialProperties: true,
    supportedEssentialProperties: [Constants.ESSENTIAL_PROP_SCHEME],
    useMediaCapabilitiesApi: false
}

ESSENTIAL_PROP_SCHEME: [
        {schemeIdUri: 'urn:mpeg:mpegB:cicp:ColourPrimaries', value: '5'},
        {schemeIdUri: 'urn:dvb:dash:fontdownload:2014', value: /.*/ }
]

From my point of view, I prefer the 2nd approach using RegEx as this utilizes only one data field in settings, however it implies an incompatibility with v4.

@dsilhavy : Please advise! I'll follow up with full code as PR

[dsilhavy]

The 2nd approach sounds much more reasonable thanks. Related pull request with further discussion: #4411

[stschr]

Resolved by: #4411