Allow a set of whitelisted HTML tags inside of i18n.defaultMessage.

[azasypkin]

As it turned out Kibana has many places where we may want to use HTML tags/elements inside of defaultMessage, e.g. long texts that include <p>, <ul> or <strong>. For example, for the long text that needs <p> we should write something like this:

<EuiText>
  <p><FormattedMessage id="visHelpText.p1" defaultMessage="P1 ..." /></p>
  <p><FormattedMessage id="visHelpText.p2" defaultMessage="P2 ..." /></p>
  <p><FormattedMessage id="visHelpText.p3" defaultMessage="P3 ..." /></p>
</EuiText>

but ideally we'd rather have something like this:

<EuiText>
  <FormattedMessage id="visHelpText" defaultMessage=`
    <p>P1 ...</p>
    <p>P2 ...</p>
    <p>P3 ...</p>
  `/>
</EuiText>

Currently it's not supported by the FormattedMessage we use for React translations (formatjs/formatjs#513), only by FormattedHTMLMessage usage of which is discouraged and that doesn't work well with textElement=React.Fragment we use to avoid additional spans.

We should define a set of text-level HTML tags (+ <a> and <img>) that we'll allow within localizable text. I like the idea that DOM Overlays rely on, maybe we can implement something similar. The solution we'll find should work for both React and Angular in a similar fashion, and, it seems, will require quite a bit of work on our end.

/cc @timroes @pavel06081991 @elastic/kibana-platform

[timroes]

@joshdover could you please explain why this got closed? Have we made a final decision not to implement this? Is this now tracked by some other issue?

[Bamieh]

@timroes We've recently closed all old stale issues. For this specific issue our intl library provides such functionality once we upgrade the package. which is something we're planning to prioratize and work on.