Blocks: Add support for variations in block.json` file

We integrated variations with block types and the corresponding REST API endpoint in #52688. It's a follow-up patch to add missing support to the `block.json` metadata file when using `register_block_type`.

Some fields for variations are translatable.Therefore, i18n schema was copied over from Gutenberg: https://github.com/WordPress/gutenberg/blob/trunk/packages/blocks/src/api/i18n-block.json. The accompanying implementation was adapted as `translate_settings_using_i18n_schema`.

Props: gwwar, swissspidy, schlessera, jorgefilipecosta.
Fixes #53238.



git-svn-id: https://develop.svn.wordpress.org/trunk@51599 602fd350-edb4-49c9-b593-d223f7449a82

tests/phpunit/data/languages/plugins/notice-pl_PL.po

@@ -2,12 +2,12 @@ msgid ""
 msgstr ""
 "Project-Id-Version: \n"
 "POT-Creation-Date: 2015-12-31 16:31+0100\n"
-"PO-Revision-Date: 2021-01-14 18:26+0100\n"
+"PO-Revision-Date: 2021-07-15 13:36+0200\n"
 "Language: pl_PL\n"
 "MIME-Version: 1.0\n"
 "Content-Type: text/plain; charset=UTF-8\n"
 "Content-Transfer-Encoding: 8bit\n"
-"X-Generator: Poedit 2.4.2\n"
+"X-Generator: Poedit 3.0\n"
 "X-Poedit-Basepath: .\n"
 "Plural-Forms: nplurals=2; plural=(n != 1);\n"
 "X-Poedit-KeywordsList: __;_e;_x:1,2c;_ex:1,2c;_n:1,2;_nx:1,2,4c;_n_noop:1,2;"
@@ -41,3 +41,15 @@ msgstr "Domyślny"
 msgctxt "block style label"
 msgid "Other"
 msgstr "Inny"
+
+msgctxt "block variation title"
+msgid "Error"
+msgstr "Błąd"
+
+msgctxt "block variation description"
+msgid "Shows error."
+msgstr "Wyświetla błąd."
+
+msgctxt "block variation keyword"
+msgid "failure"
+msgstr "niepowodzenie"