ref(detectors): Break circular dependency in metric detector search bar

[sentry]

Problem

A runtime circular dependency existed between detector dataset configuration and metric form data:
getDatasetConfig.tsx → metrics.tsx → metricsSearchBar.tsx → metricFormData.tsx → getDatasetConfig.tsx.

metricsSearchBar.tsx only needs METRIC_DETECTOR_FORM_FIELDS and useMetricDetectorFormField, but importing them from metricFormData.tsx pulled in getDatasetConfig, closing the loop.

Solution

• Extract METRIC_DETECTOR_FORM_FIELDS, useMetricDetectorFormField, and metric detector form types into a standalone metricFormFields.tsx that does not import getDatasetConfig.
• Update every consumer (including metricsSearchBar.tsx) to import the moved symbols from metricFormFields.tsx. metricFormData.tsx does not re-export them, so each symbol has one import path.
• Export PrioritizeLevelFormData from metricFormFields.tsx, because metricFormData.tsx still uses it.

Legal Boilerplate

Look, I get it. The entity doing business as "Sentry" was incorporated in the State of Delaware in 2015 as Functional Software, Inc. and is gonna need some rights from me in order to utilize my contributions in this here PR. So here's the deal: I retain all rights, title and interest in and to my contributions, and by keeping this boilerplate intact I confirm that Sentry can use, modify, copy, and redistribute my contributions, under Sentry's choice of terms.

Fixes CODING-CONVENTIONS-92W

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Cursor Bugbot has reviewed your changes and found 1 potential issue.

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[github-actions]

📊 Type Coverage Diff

Metric	Before	After	Delta
Coverage	95.72%	95.72%	±0%
Typed	142,179	142,179	±0
Untyped	6,363	6,363	±0

🔍 1 new type safety issue introduced

any-typed symbols (1 new)

File	Line	Detail
static/app/views/detectors/components/forms/metric/metricFormFields.tsx	132	value (var)

This is informational only and does not block the PR.