Add JsonNamingPolicy support to JsonConsoleFormatterOptions

[piekstra]

Fixes #125689

Summary

Adds a JsonNamingPolicy property to JsonConsoleFormatterOptions that controls the casing of built-in JSON property names emitted by JsonConsoleFormatter.

When null (default): PascalCase names are preserved — no behavioral change.
When set (e.g. JsonNamingPolicy.CamelCase): Built-in property names are transformed:

Default	CamelCase
Timestamp	timestamp
EventId	eventId
LogLevel	logLevel
Category	category
Message	message
Exception	exception
State	state
Scopes	scopes

User-provided property names from structured log state and scope data are written as-is.

Usage

builder.Logging.AddJsonConsole(options =>
{
    options.JsonNamingPolicy = JsonNamingPolicy.CamelCase;
});

Motivation

Observability platforms (New Relic, Datadog, Splunk, Grafana Loki) expect lowercase property names in structured JSON logs. The current JsonConsoleFormatter hardcodes PascalCase names with no way to change them, forcing users to write a custom ConsoleFormatter from scratch (~100 lines of boilerplate). This has been requested multiple times (#109726, dotnet/aspnetcore#58890).

Implementation notes

Property names are pre-computed in ReloadLoggerOptions (which already runs on construction and option reload) rather than calling JsonNamingPolicy.ConvertName() per log entry. This avoids per-entry overhead, though for built-in policies like CamelCase the cost would be negligible either way. The pre-computation approach was chosen because ReloadLoggerOptions is the existing pattern for applying option changes, so it's the natural place to derive the names — and it means the hot path (WriteInternal) stays allocation-free with just field reads.

Tests

Three new tests in JsonConsoleFormatterTests.cs:

• Log_JsonNamingPolicyCamelCase_ProducesCamelCasePropertyNames — verifies all built-in properties use camelCase and PascalCase names are absent
• Log_JsonNamingPolicyNull_PreservesPascalCasePropertyNames — verifies default behavior is unchanged
• Log_JsonNamingPolicyCamelCase_ScopePropertyNamesAreCamelCase — verifies scope array and inner Message key also use the naming policy

[piekstra]

@dotnet-policy-service agree

[dotnet-policy-service]

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[cincuranet]

As the #125689 adds new public API, it needs to go through API review process. I'll close this for now. We can reopen and continue when/if the API is approved.