Add raqm_bidi_engine_string() function

[akx]

Related to python-pillow/Pillow#9926: it may be useful for client software to know which bidi backend is being used.

[khaledhosny]

I don't see why clients would need to care or worry about this.

[akx]

I don't see why clients would need to care or worry about this.

If libraqm + SheenBidi is 100% bit-exact with libraqm + FriBiDi, then not.

Otherwise downstream software that has "golden image" tests like Pillow does may need manual "fudge factor" adjustments like python-pillow/Pillow@9824149 (not raqm related, but FreeType feature related) because different platforms build components slightly differently.

[khaledhosny]

I don't see why clients would need to care or worry about this.

If libraqm + SheenBidi is 100% bit-exact with libraqm + FriBiDi, then not.

They are expected to be identical and we test as such. If they are not it is a bug that have to be fixed.

[akx]

In that case, this wouldn't be necessary. Thanks!