CSS Writing Modes: add tests for text-combine-upright

add rendering tests of text-combine-upright that do not requre tailored font.

* value-all-002.html
* value-all-003.html
* value-digits2-002.html
* value-digits2-003.html
* value-digits3-001.html
* value-digits3-002.html
* value-digits3-003.html
* value-digits4-001.html
* value-digits4-002.html
* value-digits4-003.html
* value-none-001.html
* reference/horizontal-ahem-1x1-notref.html
* reference/horizontal-ahem-1x3-notref.html
* reference/horizontal-ahem-1x4-notref.html
* reference/horizontal-ahem-1x5-notref.html
* reference/vertical-ahem-1x1-ref.html
* reference/vertical-ahem-1x3-ref.html
* reference/vertical-ahem-1x4-ref.html
* reference/vertical-ahem-1x5-ref.html

Note that value-all-001.html and value-digits2-001.html are missing: these require a font.

BUG: https://github.com/w3c/csswg-test/issues/568