Add array type to fields in Highlight and default in HighlighterTagsSchema

[karenyrx]

Description

1. tags schema is missing "default" option

2. Fields supports object or array type. If object type, then useExplicitFieldOrder is set to false. If array type, then true. Code path:

• https://github.com/opensearch-project/OpenSearch/blob/main/server/src/main/java/org/opensearch/search/fetch/subphase/highlight/HighlightBuilder.java#L301
  -> https://github.com/opensearch-project/OpenSearch/blob/main/server/src/main/java/org/opensearch/search/fetch/subphase/highlight/HighlightBuilder.java#L295
  -> https://github.com/opensearch-project/OpenSearch/blob/main/libs/core/src/main/java/org/opensearch/core/xcontent/ObjectParser.java#L498-L532 )

1. JSON parser encounters "fields": ...
2. Checks if it's { (object) or [ (array)
3. If [ (array) → calls orderedModeCallback → sets useExplicitFieldOrder(true)
5. If { (object) → callback never called → useExplicitFieldOrder stays false

Issues Resolved

List any issues this PR will resolve, e.g. Closes [...].

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Changes Analysis

Commit SHA: 0e0424a
Comparing To SHA: 5432cfd

API Changes

Summary

└─┬Components
  ├──[➕] schemas (51137:7)
  └─┬_core.search___HighlighterTagsSchema
    └──[➕] enum (51121:11)

Document Element	Total Changes	Breaking Changes
components	2	0

• Total Changes: 2
• Additions: 2

Report

The full API changes report is available at: https://github.com/opensearch-project/opensearch-api-specification/actions/runs/20044558752/artifacts/4803713483

API Coverage

	Before	After	Δ
Covered (%)	666 (65.23 %)	666 (65.23 %)	0 (0 %)
Uncovered (%)	355 (34.77 %)	355 (34.77 %)	0 (0 %)
Unknown	129	129	0

[github-actions]

Spec Test Coverage Analysis

Total	Tested
682	680 (99.71 %)