Extend support of multiple columns in fulltext index

[kungasc]

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Description for reviewers

In addition to #24439.

I've realized, that some text columns may be simultaniously used as fulltext and as keys (for example git/arcradia branches).

So, I've propose to transform FulltextIndexSettings.columns list into all index key columns, not only fulltext ones.

This allows us to make this syntax work (title column is indexed in two ways):

INDEX my_index GLOBAL SYNC USING fulltext ON (
    title WITH (tokenizer = "standard", language = "russian"),
    title,
    content WITH (tokenizer = "keyword", language = "english")
) 
WITH (layout = "flat")

Also separated columns list validation for better readability.

[github-actions]

⚪ 2025-09-18 14:23:10 UTC Pre-commit check linux-x86_64-release-asan for c90fed8 has started.
⚪ 2025-09-18 14:23:14 UTC Artifacts will be uploaded here
⚪ 2025-09-18 14:27:28 UTC ya make is running...
🟡 2025-09-18 17:35:44 UTC Some tests failed, follow the links below. This fail is not in blocking policy yet

Test history | Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
18427	17483	0	487	423	34

🟢 2025-09-18 17:37:20 UTC Build successful.

[github-actions]

⚪ 2025-09-18 14:25:45 UTC Pre-commit check linux-x86_64-relwithdebinfo for c90fed8 has started.
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Details

Test history | Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
41323	38555	0	5	2725	38

⚪ 2025-09-18 16:46:32 UTC ya make is running... (failed tests rerun, try 2)
🟡 2025-09-18 17:00:17 UTC Some tests failed, follow the links below. Going to retry failed tests...

Details

Test history | Ya make output | Test bloat | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
594 (only retried tests)	569	0	1	3	21

⚪ 2025-09-18 17:00:29 UTC ya make is running... (failed tests rerun, try 3)
🟢 2025-09-18 17:09:22 UTC Tests successful.

Test history | Ya make output | Test bloat | Test bloat | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
224 (only retried tests)	204	0	0	0	20

🟢 2025-09-18 17:09:29 UTC Build successful.

[github-actions]

⚪ 2025-09-19 11:24:41 UTC Pre-commit check linux-x86_64-relwithdebinfo for 5061d00 has started.
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⚪ 2025-09-19 11:29:01 UTC ya make is running...
⚫ 2025-09-19 12:16:44 UTC Check cancelled

[github-actions]

⚪ 2025-09-19 11:25:05 UTC Pre-commit check linux-x86_64-release-asan for 5061d00 has started.
⚪ 2025-09-19 11:25:54 UTC Artifacts will be uploaded here
⚪ 2025-09-19 11:30:27 UTC ya make is running...
⚫ 2025-09-19 12:16:43 UTC Check cancelled

[github-actions]

⚪ 2025-09-19 12:20:19 UTC Pre-commit check linux-x86_64-relwithdebinfo for 6f47a8b has started.
⚪ 2025-09-19 12:20:32 UTC Artifacts will be uploaded here
⚪ 2025-09-19 12:24:49 UTC ya make is running...
🟡 2025-09-19 14:37:31 UTC Some tests failed, follow the links below. Going to retry failed tests...

Details

Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
41184	38391	0	3	2745	45

⚪ 2025-09-19 14:41:12 UTC ya make is running... (failed tests rerun, try 2)
🟢 2025-09-19 14:56:21 UTC Tests successful.

Ya make output | Test bloat | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
753 (only retried tests)	731	0	0	1	21

🟢 2025-09-19 14:56:31 UTC Build successful.

[github-actions]

⚪ 2025-09-19 12:20:43 UTC Pre-commit check linux-x86_64-release-asan for 6f47a8b has started.
⚪ 2025-09-19 12:20:56 UTC Artifacts will be uploaded here
⚪ 2025-09-19 12:25:08 UTC ya make is running...
🟡 2025-09-19 15:10:04 UTC Some tests failed, follow the links below. This fail is not in blocking policy yet

Ya make output | Test bloat

TESTS	PASSED	ERRORS	FAILED	SKIPPED	MUTED?
18219	17772	0	109	298	40

🟢 2025-09-19 15:11:36 UTC Build successful.