Fixed sortvector issue with string as key in C#

[whitecostume]

@neoblazes I am not entirely clear on what you're trying to do. What is the index, and how is it broken?我不太清楚你想做什么。索引是什么？它是怎么坏的？
Sorting an existing FlatBuffer in-place, or generally modifying an existing FlatBuffer is difficult, you should want to sort it before creating it.对现有的 FlatBuffer 进行排序或通常修改现有的 FlatBuffer 很困难，您应该在创建它之前对其进行排序。

What he meant is that a json file that has been sorted by key becomes an unordered file after being exported as a binary file by flatc, which means that SortedVector cannot be used to find the corresponding data (when the key is a string)

I found out that it was a problem with string.CompareTo #8547

Originally posted by @whitecostume in #186
Fixed sortvector issue with string as key in C# #8547