test(gutenberg-to-portable-text): add transform tests (#332)

* test(gutenberg-to-portable-text): add transform tests

This adds a bunch of tests, mostly for the transformers but also some
minor edge cases in the inline parser, too.

It also enables `noUnusedLocals` in `tsconfig.json` which caught a
couple of unused things.

* chore: add domain to each

* style: format

* chore: remove some figures

---------

Co-authored-by: emdashbot[bot] <emdashbot[bot]@users.noreply.github.com>

packages/gutenberg-to-portable-text/tsconfig.json

@@ -12,6 +12,7 @@
 		"esModuleInterop": true,
 		"skipLibCheck": true,
 		"noUncheckedIndexedAccess": true,
+		"noUnusedLocals": true,
 		"noImplicitOverride": true,
 		"verbatimModuleSyntax": true
 	},