Make ORT_TELEMETRY_DISABLED a full telemetry opt-out

[tianleiwu]

Description

Makes ORT_TELEMETRY_DISABLED a full telemetry opt-out on the non-Windows (1DS) provider. Previously, setting the environment variable only flipped enabled_ = false while Initialize() still created the 1DS uploader, wrote the persistent device-id file to disk, and let LogProcessInfo() upload a one-shot ProcessInfo event (it only checked logger_ != nullptr, not IsEnabled()). So a user who explicitly opted out still got an on-disk identifier and a network upload.

With this change, the env-var opt-out is treated like CI / unit-test suppression: the provider returns early before creating the uploader, so nothing is initialized, persisted, or sent.

Key Changes

File	Change
onnxruntime/core/platform/telemetry_environment.h	ShouldSuppressTelemetry() now also returns true for IsTelemetryDisabledByEnvVar(), making it the single "collect nothing" gate.
onnxruntime/core/platform/posix/telemetry.cc	Initialize() collapses the CI/unit-test and env-var checks into one early return on ShouldSuppressTelemetry(). When set, no LogManager/uploader is created, DeviceId::GetValue() is never called (no device-id file), and LogProcessInfo() returns early (no upload). env_disabled_ is still latched so the runtime EnableTelemetryEvents() API cannot re-enable it. LogProcessInfo() comment updated.
docs/Privacy.md	Documents the env-var as a full opt-out: no uploader, no init event, no persistent device id, latched for the process lifetime.
onnxruntime/test/platform/telemetry_environment_test.cc	Adds assertions that ShouldSuppressTelemetry() is true when ORT_TELEMETRY_DISABLED is set.

Motivation and Context

Addresses review feedback on #27379 (the "opt-out asymmetry" thread): an explicit ORT_TELEMETRY_DISABLED=1 should leave no on-disk identifier and send nothing, rather than only suppressing usage events while still emitting an initialization heartbeat. The runtime API-based disable (DisableTelemetryEvents()) is unchanged and may still emit a minimal init event, matching the Windows ETW model.

Testing

• TelemetryEnvironmentTest.EnvVarOptOut now asserts full suppression via ShouldSuppressTelemetry().
• Verify on a non-Windows telemetry build that with ORT_TELEMETRY_DISABLED=1: no onnxruntime.db/deviceid file is created under the cache dir, and no ProcessInfo event is uploaded.