[C# 14-Errors and warnings]: New Feature - projectless compile

[BillWagner]

Visual Studio release

other - specify below

Link to speclet

• Speclet

Link to Pull request

• PR

Errors and warnings added for this feature

• CS9297
• CS9298
• CS9299
• CS9314

In addition, combine other errors and warnings related to preprocessor symbols. I wanted to separate this out from #46376 due to scope.

What language theme applies, for consolidation of articles

No response

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Associated WorkItem - 436518