Feature: use gon object to show spantree

[maxming2333]

Although there is no gon object on the obtained window object

but the gon content text information can be obtained through document.innerHTML

so that it can be judged whether it is a gitlab page.

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By the way, some of the methods for obtaining gon object judgment mentioned in issues can also be obtained using the document.innerHTML + regular expression method.

[maxming2333]

@tavyandy97 This does not modify the previous judgment, it just adds a judgment method, which can work normally in my GitLab Community Edition 14.2.6