Query docs for custom operators don't mention they are custom operators

The [query docs for each custom operator](https://fsharp.github.io/fsharp-core-docs/reference/fsharp-linq-querybuilder.html) need a `remarks` section (or a mention in the summary) about how the custom opreator is used

At the moment there's no mention of the custom operator, and the usage text looks like a method call.

Two sides to this

* partly an FSharp.Core.xml problem (doc comment needs to mention this)

* partly an F#F problem (adjust usage text to show both method call and builder syntax)


先查看 issue 中連結的查詢文件和相關的 FSharp.Core.xml 文件註解，然後檢查 FSharp.Formatting 如何產生用法文字。更新文件，使每個自訂運算子都獲得識別，且其用法同時顯示方法呼叫語法和建構器語法；產生的查詢文件反映這兩種形式時即完成。

由索引模型根據 Issue 內容生成。