[release/6.0] Fix diff checks for ContentRoot and WebRoot

[halter73]

Prevent unnecessary startup errors in WebApplicationBuilder

Without this fix, when a wwwroot directory exists, calling the builder.WebHost.ConfigureAppConfiguration() method throws a NotSupportedException error thinking the web root directory (wwwroot by default) was modified when it wasn't.

Description

Backport of #40095. #38212 (comment) brought this back to my attention.

Customer Impact

Normally we'd tell customers to use builder.Configuration instead of builder.WebHost.ConfigureAppConfiguration(), but builder.WebHost is an IWebHostBuilder adapter for many extension methods like .UseStaticWebAssets().

This bug causes .UseStaticWebAssets() and just about any other method calling ConfigureAppConfiguration() to throw a NotSupportedException when it shouldn't. There is a workaround, but it's hard to discover and shouldn't be necessary.

var builder = WebApplication.CreateBuilder(args);
builder.WebHost.UseStaticWebAssets(); // Throws NotSupportedException today
builder.WebHost.UseWebRoot("wwwroot").UseStaticWebAssets(); // Works

Fixes #39546 and #38212

Regression?

• Yes
• No

Risk

• High
• Medium
• Low

This change has automated tests and was fixed in 7.0-preview2 and verified by customers.

Verification

• Manual (required)
• Automated

Packaging changes reviewed?

• Yes
• No
• N/A

[ghost]

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[ghost]

Hi @halter73. Please make sure you've updated the PR description to use the Shiproom Template. Also, make sure this PR is not marked as a draft and is ready-to-merge.

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[adityamandaleeka]

@halter73 Has this been sent to tactics?