fix: translate SIMILAR TO pattern to PostgreSQL-compatible regex

[Dandandan]

Which issue does this PR close?

• Closes PostgreSQL compatibility: SIMILAR TO should treat % as a wildcard #22263.

Rationale for this change

SIMILAR TO is supposed to mix SQL LIKE wildcards (%, _) with POSIX regex metacharacters and match the entire string. DataFusion was lowering SIMILAR TO directly to a RegexMatch over the pattern verbatim, so:

• 'abc' SIMILAR TO 'a%' returned false (PG: true) because % was passed through as a literal regex character.
• 'abc' SIMILAR TO 'b' returned true (PG: false) because the regex match isn't anchored.
• ., ^, $ were treated as regex metacharacters instead of literals.

What changes are included in this PR?

• New translate_similar_to_pattern() helper in datafusion/physical-expr/src/expressions/binary.rs that converts a SIMILAR TO pattern into an equivalent POSIX regex:
  • Anchors the result with ^...$.
  • % → .*, _ → ..
  • Escapes ., ^, $ (literal in SIMILAR TO, meta in regex).
  • Passes POSIX metas (|, *, +, ?, (), {m,n}, [...]) through unchanged.
  • Handles \ as an escape for the next character.
  • Passes bracket expressions through verbatim, including a leading literal ]/^].
• Planner (datafusion/physical-expr/src/planner.rs) now translates literal Utf8 / LargeUtf8 / Utf8View patterns at planning time. NULL patterns flow through as a typed Utf8 null. Non-literal patterns return a clear not_impl_err rather than the previous silently-wrong behavior.
• SQL layer (datafusion/sql/src/expr/mod.rs) pattern-type check widened to accept LargeUtf8 and Utf8View literals (previously rejected even though the underlying regex match supports them).

Are these changes tested?

Yes:

• Unit test similar_to_pattern_translation in binary.rs covers wildcards, anchoring, regex metas, literal ./^/$, backslash escapes, bracket expressions (including []abc] and [^]abc]).
• datafusion/sqllogictest/test_files/strings.slt has a new regression block exercising the bug-report case, _ wildcard, anchoring, literal ./^/$, regex metas (|, {m,n}, +), backslash-escaped wildcards, NULL pattern, and the non-literal-pattern error.
• The existing SIMILAR TO 'p[12].*' test in strings.slt was relying on the buggy regex-passthrough behavior (p1e1 etc. matched only because . was treated as regex .); it's been changed to 'p[12]%' which expresses the same intent under correct SIMILAR TO semantics.

Are there any user-facing changes?

Yes — SIMILAR TO is now PostgreSQL-compatible:

• Behavior changes for patterns containing %, _, or unanchored matches. Existing patterns that relied on the previous regex-passthrough behavior may need to be updated (most obviously, change .* to %).
• Non-literal patterns now return Not yet implemented: SIMILAR TO with a non-literal pattern is not yet supported instead of silently returning a regex match. This was almost certainly broken in practice already, but it is a visible error message change.