Add docs for CA1865/CA1866/CA1867

[mrahhal]

Implementation PR: dotnet/roslyn-analyzers#6799

---

Internal previews

📄 File	🔗 Preview link
docs/core/whats-new/dotnet-8.md	What's new in .NET 8
docs/fundamentals/code-analysis/quality-rules/ca1865-ca1867.md	docs/fundamentals/code-analysis/quality-rules/ca1865-ca1867
docs/fundamentals/code-analysis/quality-rules/index.md	Code quality rules overview
docs/fundamentals/code-analysis/quality-rules/performance-warnings.md	Performance rules

[mrahhal]

Didn't know multiple rules can be put in the same file, as in the case of syslib1040-1049. Should these three rules similarly be in the same file?

[gewarren]

@mrahhal Yes I think it's better to put these in one file. You'll also need to add redirections similar to:

docs/.openpublishing.redirection.fundamentals.json

Lines 196 to 205 in b4c2946

	"source_path_from_root": "/docs/fundamentals/syslib-diagnostics/syslib1040.md",
	"redirect_url": "/dotnet/fundamentals/syslib-diagnostics/syslib1040-1049"
	},
	{
	"source_path_from_root": "/docs/fundamentals/syslib-diagnostics/syslib1041.md",
	"redirect_url": "/dotnet/fundamentals/syslib-diagnostics/syslib1040-1049"
	},
	{
	"source_path_from_root": "/docs/fundamentals/syslib-diagnostics/syslib1042.md",
	"redirect_url": "/dotnet/fundamentals/syslib-diagnostics/syslib1040-1049"