feat(duckdb): Add transpilation support for neg position args for CHARINDEX

[fivetran-amrutabhimsenayachit]

CHARINDEX did not transpile as expected for neg position arg.
This PR fixes the same.

snow sql -q "SELECT CHARINDEX('l', 'hello world', -2)"
 CHARINDEX('L', 'HELLO WORLD', -2) |
|-----------------------------------|
| 3                                 |

python -m sqlglot --read snowflake --write duckdb "SELECT CHARINDEX('l', 'hello world', -2)"
SELECT
  CASE
    WHEN STRPOS(SUBSTRING('hello world', CASE WHEN -2 <= 0 THEN 1 ELSE -2 END), 'l') = 0
    THEN 0
    ELSE STRPOS(SUBSTRING('hello world', CASE WHEN -2 <= 0 THEN 1 ELSE -2 END), 'l') + CASE WHEN -2 <= 0 THEN 1 ELSE -2 END - 1
  END
  
Duckdb Result
│      3 │

[github-actions]

SQLGlot Integration Test Results

Comparing:

• this branch (sqlglot:RD-1147696-charindex, sqlglot version: RD-1147696-charindex)
• baseline (main, sqlglot version: 0.0.1.dev1)

⚠️ Limited to dialects: duckdb, snowflake

By Dialect

dialect	main	sqlglot:RD-1147696-charindex	transitions	links
duckdb -> duckdb	4003/4004 passed (100.0%)	4003/4004 passed (100.0%)	No change	full result / delta
snowflake -> duckdb	1508/2674 passed (56.4%)	1508/2674 passed (56.4%)	No change	full result / delta
snowflake -> snowflake	65910/65910 passed (100.0%)	65910/65910 passed (100.0%)	No change	full result / delta

Overall

main: 72588 total, 71421 passed (pass rate: 98.4%), sqlglot version: 0.0.1.dev1

sqlglot:RD-1147696-charindex: 72588 total, 71421 passed (pass rate: 98.4%), sqlglot version: RD-1147696-charindex

Transitions:
No change

[geooo109]

We should apply the logic on the transpiled query, right ?

WITH t as (select -1 as p) SELECT CHARINDEX('l', 'hello world', p) from t

We don't cover this ^ case. On parse time we don't know the value of p.