Fixes #3753 update aspnet/core/security/authentication/social/ for 2.0

[01binary]

Fixes #3753 update aspnet/core/security/authentication/social/ for 2.0.

• Update provider steps
• Update ASP.NET Core code snippets
• Replace complex inline sections with references to separately maintained topics that would do a better job
• Update screenshots (shadows replaced with borders to handle light/dark theme switch)
• Expect QA/wording/markdown pass from @RickAndMSFT
• All steps verified as actually working but could use a light QA pass from someone intimately familiar with social provider configuration in places where technical details are described

[dnfclas]

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[Rick-Anderson]

@01binary looks fantastic. Can you take a quick look at my commits to make sure I didn't break anything?

[01binary]

I think I missed something in the markdown:

html.ValidateBookmark](security/authentication/social/google-logins.md#L125)Illegal link: [earlier on this page](#enable-googleplus) -- missing bookmark. The file security/authentication/social/google-logins.md doesn't contain a bookmark named enable-googleplus.

Looks good other than that.

[01binary]

On the Google provider page, all the Notes are broken. All other pages seem to have them working.

[EDIT]

I will leave this one to you because the intention is not clear. If you like making notes with ">" and "[!NOTE]" on the first line, then Google can be updated to fix these missing tokens on 87-95 and 105 in google-logins.md

[Rick-Anderson]

@01binary The internal build looks great. I removed a bunch of the obtrusive [!NOTE] > markup and replaced it by regular text.