[ML] Increase Test Coverage 7.13

[walterra]

Follow up to #88811.

Meta issue to summarize improvements to test coverage for 7.13.

Jest unit tests

• x-pack/plugins/transform/server/routes/api/transforms_nodes.test.ts [ML] Transforms: Fixes missing number of transform nodes and error reporting in stats bar. #93956 — isNodes() type guard tests
• x-pack/plugins/ml/common/constants/messages.test.ts [ML] Anomaly Detection: Migrate validation messages links to use docLinks. #94568 — client side unit tests for job validation messages
• x-pack/plugins/ml/public/application/data_frame_analytics/pages/analytics_management/components/source_selection/source_selection.test.tsx [ML] Data Frame Analytics: Don't allow user to pick an index pattern or saved search based on CCS. #96555 — Tests for the SourceSelection component behavior in regards to CCS

API integration tests

part of #63700

• /api/ml/data_frame/analytics/_explain [ML] API Integration tests: adds test for Data Frame Analytics explain endpoint #98060 (MA)
• /api/ml/data_frame/_evaluate [ML] API Integration tests: adds test for Data Frame Analytics evaluate endpoint #97856 (MA)
• /api/ml/jobs/datafeed_preview [ML] Adding additional runtime mapping checks #94760 (JG)
• /api/ml/notification_settings (no longer used, removed [ML] removing unused notification settings endpoint #98109 (JG)
• /api/transform/transforms/_nodes [ML] Transforms: Fixes missing number of transform nodes and error reporting in stats bar. #93956 (WR)

Functional tests

• Stabilize canvas element tests [ML] Functional Tests: Extend canvas assertion options. #91473 (WR)
• Transform runtime mappings [ML] Add functional tests for runtime mappings in Transforms #92738 (QN)
• Swim lanes [ML] Functional tests for Anomaly swim lane  #94723 (DA)
• Anomaly chart embeddable [ML] Add Anomaly Explorer charts embeddable #94396 (QN)
• DFA runtime mappings [ML] Data Frame Analytics: adds functional tests for runtime fields support #96262 (MA)
• Anomalies table change page size [ML] Check for the sort field type in Anomalies table before updating the URL state. #98270 (DA)
• Analytics list row expansion content [ML] Functional tests for Analytics list row expansion content #98678 (QN)

Accessibility tests

part of #88496

• Transform accessibility tests [ML] Transforms: Adds a11y tests for Transform plugin #93197 (PH)

[elasticmachine]

Pinging @elastic/ml-ui (:ml)

[peteharverson]

Closing issue. Remaining items have been moved to the 7.14 issue #97982.