…ant like Elasticsearch (#69825)

### What problem does this PR solve?

Issue Number: None

Related PR: #69815, #69269

Problem Summary: score() of pattern queries disagrees with Elasticsearch
and with itself on branch-4.1:

    -- 'Inverted indexes are suitable for full text search',
    -- 'The parser splits text into multiple terms', ...
SELECT score() FROM document WHERE SEARCH('content:/.*ext/'); -- BM25
sum
SELECT score() FROM document WHERE SEARCH('content:*ext'); -- BM25 sum
    SELECT score() FROM document WHERE content MATCH_REGEXP 'ext'; -- 0

Elasticsearch scores a query_string /regexp/, wildcard or prefix, and a
regexp, wildcard or prefix query, with a constant 1 per matching row
(default rewrite constant_score_blended); measured on 9.5.5 with the
rows above: 1.0 for both matching rows. Only an explicit
"rewrite": "scoring_boolean" sums the BM25 of the expanded terms. Next
to a scored clause in a bool must, a regexp adds exactly 1.

#69269 (the branch-4.1 pick of #69052) made SEARCH regexp and wildcard
sum the BM25 of every expanded term, i.e. scoring_boolean always on,
with idf and avgdl taken from the current segment rather than the tablet
statistics MATCH uses, so identical rows in two segments scored
differently. MATCH_REGEXP never requested a scoring context, so it
scored 0 like a filter.

Fix, the same as #69815 on master:
1. Revert #69269: RegexpWeight scores every pattern with the constant
   scorer again; its suite that pinned the BM25 sums is removed.
2. MATCH_REGEXP requests scoring on every index, and the legacy
   RegexpQuery records 1 for every matching row when score() is
   requested. The MATCH statistics collector skips it, since a constant
   reads no statistics and the pattern is not text to analyze.

A MATCH_REGEXP on a keyword (untokenized) index also scores 1 once the
keyword reader requests scoring (#69791); until then it keeps 0.

### Release note

score() of SEARCH regexp and wildcard clauses is a constant 1 per
matching row again, like prefix clauses and Elasticsearch's default.
score() of MATCH_REGEXP on a tokenized index is 1 instead of 0.

### Check List (For Author)

- Test: Regression test / Unit Test / Manual test
    - Regression test: new search/test_search_score_pattern_constant
      (V2/V3, two segments); all 18 blocks equal the master PR's V2/V3
      blocks; 16 existing score suites in inverted_index_p0 and search
      pass unchanged
- Unit Test: 130 tests (IndexReaderHelperTest, CollectionStatistics*,
      RegexpQueryTest and the query_v2 regexp/wildcard tests restored by
      the revert)
    - Manual test: Elasticsearch 9.5.5 on the same rows; a two-segment
table now scores 1 for every pattern hit on a branch-4.1 ASAN build
- Behavior changed: Yes. SEARCH regexp/wildcard scores and MATCH_REGEXP
  scores change as described in the release note.
- Does this need documentation: No


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Co-authored-by: Claude Opus 5.5 <[email protected]>