Bug 1898892 - Use nsIDocumentEncoder.OutputFormatted as required by a Debug assert. r=#thunderbird-reviewers

I do not know why m-c requires using `OutputFormatted` in order to use
`OutputFormatFlowed`. To resolve the test fail, this fix is adding the
required flag. However, this is not really what I want, since
`OutputFormatted` translates `<b>` tags to `*` and `<i>` tags to `/`.

Will ask m-c if this requirement could be lifted.

See: https://searchfox.org/mozilla-central/rev/f967675ec87bb200b5b911b6fd0fb8c1e06c5167/dom/serializers/nsPlainTextSerializer.cpp#323-328

Differential Revision: https://phabricator.services.mozilla.com/D211660

--HG--
extra : amend_source : 391d4f20af554997a34414b7f5b3876532c29276

mail/components/extensions/parent/ext-utilities.js

@@ -38,7 +38,7 @@ this.messengerUtilities = class extends ExtensionAPIPersistent {
           if (options?.flowed) {
             wrapWidth = 72;
             flags |=
-              Ci.nsIDocumentEncoder.OutputWrap |
+              Ci.nsIDocumentEncoder.OutputFormatted |
               Ci.nsIDocumentEncoder.OutputFormatFlowed;
           }
 

mail/components/extensions/test/xpcshell/test_ext_utilities.js

@@ -197,7 +197,7 @@ add_task(async function test_convertToPlainText() {
             // Flowed output is wrapping lines to 72 chars length. The enforced
             // line breaks have a trailing space, allowing the client to reflow
             // the text and only honor the line breaks added by the user.
-            expectedPlain: `This is flowed html content,
+            expectedPlain: `This is /flowed/ html content,
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