fix(search): remove stale facet metadata

[dschmidt]

Summary

Fixes #3677.
The indexer already stats the resource, so it can compare the stored libre.graph.<facet>.* keys with the fresh extraction.

 doUpsertItem
   stat, extract, index
+  UnsetArbitraryMetadata(stored facet keys the extraction no longer delivers)
+  drop facet keys whose stored value is unchanged
   if no facet metadata: return
   SetArbitraryMetadata(facet keys)

Reindexing an unchanged file no longer writes to the storage. Existing leftovers disappear on the next reindex of the file.

[codacy-production]

Up to standards ✅

🟢 Issues 0 issues

Results:
0 new issues

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🟢 Metrics 19 complexity

Metric	Results
Complexity	19

View in Codacy

🟢 Coverage 82.14% diff coverage · +0.05% coverage variation

Metric	Results
Coverage variation	✅ +0.05% coverage variation (-1.00%)
Diff coverage	✅ 82.14% diff coverage

View coverage diff in Codacy

Coverage variation details

	Coverable lines	Covered lines	Coverage
Common ancestor commit (371e84b)	91169	22413	24.58%
Head commit (d924ea1)	91197 (+28)	22468 (+55)	24.64% (+0.05%)

Coverage variation is the difference between the coverage for the head and common ancestor commits of the pull request branch: <coverage of head commit> - <coverage of common ancestor commit>

Diff coverage details

	Coverable lines	Covered lines	Diff coverage
Pull request (#3682)	28	23	82.14%

Diff coverage is the percentage of lines that are covered by tests out of the coverable lines that the pull request added or modified: <covered lines added or modified>/<coverable lines added or modified> * 100%

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