Update CursorParser to use '\' as escape instead of ':'

[onionhammer]

TL;DR - There's a bug where HotChocolate cannot parse the pagination cursors it generates if the cursor is ordering on a string, and the string contains a ':' character.

When HotChocolate encodes a cursor with multiple keys, if one of the keys is a string containing a ':', it will attempt to encode the colon with a backslash (\), when HotChocolate decodes the cursor, there is a bug where ':' is the escape character.

This pull request switches the escape character defined in CursorParser to be '' instead of ':'

I have updated some existing tests to cover having a colon embedded in the names being sorted on - these tests fail now without this code change.

The cursor value is not a valid guid
at HotChocolate.Pagination.Serialization.GuidCursorKeySerializer.Parse(ReadOnlySpan1 formattedKey) at HotChocolate.Pagination.Serialization.CursorKeySerializerHelper.Parse(ReadOnlySpan1 formattedKey, ICursorKeySerializer serializer)
at HotChocolate.Pagination.Expressions.CursorKey.Parse(ReadOnlySpan1 cursorValue) at HotChocolate.Pagination.Expressions.CursorParser.Parse(String cursor, ReadOnlySpan1 keys)
at HotChocolate.Data.Pagination.EfQueryableCursorPagingHandler1.SliceAsync(IResolverContext context, IQueryableExecutable1 executable, CursorPagingArguments > arguments)
at HotChocolate.Types.Pagination.CursorPagingHandler.HotChocolate.Types.Pagination.IPagingHandler.SliceAsync(IResolverContext context, Object source)
at HotChocolate.Types.Pagination.PagingMiddleware.InvokeAsync(IMiddlewareContext context)