Add Arabic support

[mustakshif]

Feature or bug? 特性或者缺陷？

If you want to contribute a feature or bug fix, please submit an issue first. After a full discussion in the community, we will decide whether to make the change. Do not submit a contribution code directly, otherwise it may be rejected.
如果你想贡献一个特性或者缺陷修复，请先提交一个 issue。在社区充分讨论后，我们会决定是否进行变更。不要直接提交一个贡献代码，否则可能会被拒绝。

Multilingual or copywriting? 多语言或者文案？

Please submit directly, we will evaluate.
请直接提交，我们会进行评估。

Dev branch!

Any changes should be submitted to the dev branch.
任何改动，请提交到 dev 分支。

[mustakshif]

This PR adds Arabic language support to SiYuan. I've performed initial testing locally. Please review.

[TCOTC]

Please make sure all placeholders are of the form ${...}

I tried it and it seems that using {...}$ will not cause problems

[mustakshif]

Please make sure all placeholders are of the form ${...}

I tried it and it seems that using {...}$ will not cause problems

This is expected behavior when displaying RTL languages in an LTR context. While the visual representation might appear unusual to humans, the text will parse correctly as long as the character sequence is maintained in the proper order.

[88250]

感谢你的贡献，思源有你更精彩！
Thank you for your contribution. SiYuan will be more wonderful with you!