[Mobile]Improve accessibility on Heading block

[pinarol]

Description

This PR improves accessibility on Heading block.
Fixes wordpress-mobile/gutenberg-mobile#908

To test:
Please refer to the gutenberg-mobile side PR.

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.

[etoledom]

Tested via wordpress-mobile/gutenberg-mobile#925 (review)

Great job!

[swissspidy]

@etoledom @pinarol Why exactly is this not using sprintf()? I am afraid these strings are totally not translatable this way.

[swissspidy]

Opened #15161 for this.

[pinarol]

@etoledom @pinarol Why exactly is this not using sprintf()? I am afraid these strings are totally not translatable this way.

Thanks for the heads-up @swissspidy These are the strings to be read out loudly by screen readers(as a part of device accessibility), we just wanted to put a pause between the words and it is done by dot+space. So we didn't want to derive new strings just to put '. ' after them. BTW I totally agree that 'level' should be fixed as 'level %s', that's sth we missed. So, if deriving new strings is the more preferred way by translators that's perfectly ok for us, and it is easier for us to code too!

[swissspidy]

Thanks for the additional context. Yes, I would say in this case new strings is better. String concatenation does not work for every language there is, and a complete sentence is much easier to comprehend for translators.