Fix static field documentation to clarify storage behavior for generic types

[Copilot]

The documentation incorrectly stated that there is "only one copy" of each static field, which is misleading for generic types. For generic types, each closed generic type (e.g., MyClass<int> vs MyClass<string>) has its own separate storage location for static fields.

Changes Made

Updated three documentation files to add clarifying language about static field storage in generic types:

• docs/csharp/language-reference/keywords/static.md - Added clarification after the statement about "only one copy of each static field"
• docs/csharp/programming-guide/classes-and-structs/static-classes-and-static-class-members.md - Added clarification in the "Static Members" section
• docs/csharp/misc/cs1914.md - Added clarification in the compiler error documentation

Example

class MyClass<T>
{
    static int count;
}

// These are separate storage locations:
MyClass<int>.count = 1;
MyClass<string>.count = 2;
// MyClass<int>.count is still 1, MyClass<string>.count is 2

The changes are minimal and surgical, preserving the existing content while adding the necessary clarification. The terminology continues to use "static field" as recommended by @BillWagner, avoiding the ambiguous "class field" term.

Fixes #22805.

---

💬 Share your feedback on Copilot coding agent for the chance to win a $200 gift card! Click here to start the survey.

---

Internal previews

📄 File	🔗 Preview link
docs/csharp/language-reference/keywords/static.md	docs/csharp/language-reference/keywords/static
docs/csharp/misc/cs1914.md	docs/csharp/misc/cs1914
docs/csharp/programming-guide/classes-and-structs/static-classes-and-static-class-members.md	docs/csharp/programming-guide/classes-and-structs/static-classes-and-static-class-members

[BillWagner]

This LGTM after responding to @jkotas 's feedback.