[9.1] fix: dynamic template vector array is overridden by automatic dense_vector mapping (#143733)

[salvatore-campagna]

Backport Note

This is a backport of #143733 to 9.1, identical to the 8.19 backport in #143985.

This backport is needed because the rest-compatibility CI check (yamlRestCompatTest) on the 9.1 branch fails for any PR due to the missing fix. Specifically, the test search.vectors/60_dense_vector_dynamic_mapping/Float arrays inside nested objects respect float dynamic templates and are not mapped as dense_vector was added upstream but the underlying bug fix was never backported to 9.1, causing a rest-compatibility CI failure (e.g., see #144765).

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Problem

When a float array is inside a nested object (e.g., my_object.my_float_field) and a dynamic template matches that field name (e.g., match: "*float*" with type: float), the dynamic template is not respected. Instead, the array is automatically mapped as dense_vector.

The root cause is in DynamicFieldsBuilder.createDynamicField(): markFieldAsAppliedFromTemplate(name) uses the short field name (my_float_field), but the automatic dense_vector mapping check uses the full path (my_object.my_float_field). Since they don't match, the "applied from template" marker is missed and the array gets auto-mapped as dense_vector.

Fix

Use context.path().pathAsText(name) instead of name when calling markFieldAsAppliedFromTemplate, so the full field path is stored and correctly matched during the dense_vector auto-detection check.

Tests

• YAML REST test: Float arrays inside nested objects respect float dynamic templates and are not mapped as dense_vector gated behind the mapper.dense_vector.dynamic_template_nested_object_fix cluster feature.

./gradlew :rest-api-spec:yamlRestTest --tests "*60_dense_vector_dynamic_mapping*Float arrays inside nested*"

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