Block Processor tests fail without intl extension

[dmsnell]

The new Block Processor test suite calls NumberFormatter without checking if it exists. It uses the class for generating test failure errors, but in environments without the intl extension it will crash.

Trac ticket: Core-64329

The Block Processor tests call NumberFormatter for generating its error messages, but in environments lacking the intl extension this led to crashes while running the tests.

This patch reworks the tests so that they avoid calling NumberFormatter so that the tests run on more diverse setups.

[dmsnell]

In 61342:

Block Processor: Remove use of NumberFormatter from test suite.

The Block Processor tests call NumberFormatter for generating its
error messages, but in environments lacking the intl extension this
led to crashes while running the tests.

This patch reworks the tests so that they avoid calling
NumberFormatter so that the tests run on more diverse setups.

Developed in ​https://github.com/WordPress/wordpress-develop/pull/10576
Discussed in https://core.trac.wordpress.org/ticket/64329

Follow-up to [60939].

Props desrosj, ellatrix, peterwilsoncc, westonruter.

See #64329.

Merged in ​https://github.com/wordpress/wordpress-develop/commit/6045c24efe16f3685c40ed9cac147ff22d5c65d2
[61342]

[dmsnell]

Adding dev-feedback keyword for backport into 6.9.1

[jonsurrell]

Approving this test fix for certain environments for backport.

[jorbin]

[61342] looks good for backport.