Update documents for field backed properties

[BillWagner]

Fixes #42820
Fixes #43224

Update and add documents relevant to field backed properties.

Commit by commit summary:

1. Add the field backed properties updates to property articles in the language reference: While doing this, update the relevant articles to lead with automatically implemented properties, followed by field backed, then expression bodied, and finally fully implemented property accessors.
2. Found more instances of "autoimplemented": This time without the hyphen.
3. Add discussion of field backed properties to all relevant programming guide and fundamentals articles.. Also, publish the feature spec for this preview feature.
4. Finalize errors and warnings: This feature added a couple error messages.
5. Consistent terminology: The other language docs use "compiler synthesized" instead of "compiler generated"

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Internal previews

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📄 File	🔗 Preview link
docs/core/whats-new/dotnet-9/overview.md	What's new in .NET 9
docs/csharp/language-reference/attributes/general.md	"Attributes interpreted by the compiler: Miscellaneous"
docs/csharp/language-reference/builtin-types/record.md	Records (C# reference)
docs/csharp/language-reference/compiler-messages/partial-declarations.md	Errors and warnings related to partial type and partial member declarations
docs/csharp/language-reference/keywords/field.md	"The field contextual keyword"
docs/csharp/language-reference/keywords/get.md	The get keyword
docs/csharp/language-reference/keywords/index.md	C# Keywords
docs/csharp/language-reference/keywords/init.md	"The init keyword - init only properties"
docs/csharp/language-reference/keywords/set.md	The set keyword (C# Reference)
docs/csharp/language-reference/keywords/value.md	docs/csharp/language-reference/keywords/value
docs/csharp/language-reference/toc.yml	docs/csharp/language-reference/toc
docs/csharp/linq/get-started/walkthrough-writing-queries-linq.md	Tutorial: Write queries in C# using language integrated query (LINQ)
docs/csharp/programming-guide/classes-and-structs/auto-implemented-properties.md	Automatically implemented properties
docs/csharp/programming-guide/classes-and-structs/object-and-collection-initializers.md	"Object and Collection Initializers"
docs/csharp/programming-guide/classes-and-structs/partial-classes-and-methods.md	Partial Classes and Methods (C# Programming Guide)
docs/csharp/programming-guide/classes-and-structs/properties.md	docs/csharp/programming-guide/classes-and-structs/properties
docs/csharp/programming-guide/classes-and-structs/restricting-accessor-accessibility.md	Restricting Accessor Accessibility (C# Programming Guide)
docs/csharp/programming-guide/classes-and-structs/using-properties.md	"Using Properties"
docs/csharp/specification/toc.yml	docs/csharp/specification/toc
docs/csharp/whats-new/csharp-13.md	What's new in C# 13

[BillWagner]

@IEvangelist @tdykstra

The work here is done. The snippets 5000 error is because the field preview feature isn't yet available in the .NET 9 SDK. It will be in the GA release. I'll wait until that goes live before merging.

[BillWagner]

.NET 9 is avaiable.