feat: standalone check for telemetry enabled

[mshanemc]

What does this PR do?

if you want to check if telemetry is enabled, there were a lot of perf-killing side effects

• requiring appInsights
• configAgg => all of sfdx-core => all of jsforce

This change

• do the enabled check in a standalone function that memoizes the result
• put the enabledCheck as a top-level export. You can import just that instead of all of exported.ts
• re-use the memoized check in the telemetryReporter class, removing the static OOP tricks needed used to persist that state (and deprecate the static method)
• since some methods aren't async, store the result in the class so sync instance methods can access it

No breaking changes intended. Verify that the pjson exports prop doesn't break consumers.

What issues does this PR fix or reference?

@W-13931029@

QA: I shipped a CLI prerel to validate with (2.5.2-qa.0)
verify things are still getting to AppInsights (hint: search using your cliid)

run DEBUG=perf sf config list a few times, looking for something like @salesforce/plugin-telemetry(./lib/hooks/telemetryPrerun.js): 312.1893ms