i18n xlf alt-trans tag is used instead of target

[crtl]

🐞 bug report

Affected Package

@angular/i18n

Description

After extracting the translations as xlf files and editing them in my translation tool angular cannot use the translations correctly anymore. The translation tool adds tags inside the document which angular then reads instead of the actual translation.

In the following example angular displays Content (trans-unit > alt-trans > target) instead of Weiter (trans-unit > target)

🔬 Minimal Reproduction

<!-- messages.de.xml -->
<trans-unit datatype="html" approved="no" id="registration.submit">
   <source>
      Continue
   </source>
   <target state="translated" xml:lang="de">Weiter</target>
   <context-group purpose="location">
      <context context-type="sourcefile">src/app/auth/registration-form/registration-form.component.html</context>
      <context context-type="linenumber">69</context>
   </context-group>
   <?sid 1110954287-0?>
   <alt-trans origin="autoFuzzy" tool="Swordfish" match-quality="71" ts="63">
      <source xml:lang="en">Content</source>
      <target state="translated" xml:lang="de">Content</target>
   </alt-trans>
</trans-unit>

<button type="submit" class="btn btn-submit" i18n="@@registration.submit">
   Continue
</button>

🌍 Your Environment

Angular Version:

Package                           Version
-----------------------------------------------------------
@angular-devkit/architect         0.803.4
@angular-devkit/build-angular     0.803.4
@angular-devkit/build-optimizer   0.803.4
@angular-devkit/build-webpack     0.803.4
@angular-devkit/core              8.3.4
@angular-devkit/schematics        8.3.6
@angular/cli                      8.3.6
@ngtools/webpack                  8.3.4
@schematics/angular               8.3.6
@schematics/update                0.803.6
rxjs                              6.4.0
typescript                        3.5.3
webpack                           4.39.2

Anything else relevant?
Swordfish III used for translations.

[petebacondarwin]

@crtl can you confirm that this is with ivy disabled?

[petebacondarwin]

#33450 will fix this.

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