Parse SQL92 create column nullability

[iamhucong]

Fix SQL92 CREATE TABLE column nullability metadata.

Problem

The SQL92 grammar accepts column-level NOT NULL and NULL options, but SQL92DDLStatementVisitor.visitColumnDefinition() always constructed ColumnDefinitionSegment with notNull=false.

Change

• Derive notNull from the parsed NOT NULL option.
• Add a focused SQL92 parser case covering NOT NULL and explicit NULL.
• Add the ShardingSphere 5.5.4 bug-fix release note.

Verification

• Baseline: InternalSQL92ParserIT passed 207 tests.
• InternalSQL92ParserIT: 208 tests passed after the change.
• SQL92 parser module passed.
• Spotless passed.
• Checkstyle reported 0 violations.
• git diff --check passed.

[iamhucong]

Code Correctness Review

Review Result: Mergeable

PR #39439 correctly preserves SQL92 CREATE TABLE column nullability metadata. No code-correctness blockers were found.

Evidence

• Reviewed the latest public head 464028e2dd9dc9878dc6652dbb3618e4de2316f6.
• The SQL92 grammar accepts NOT NULL and NULL through dataTypeOption at parser/sql/engine/dialect/sql92/src/main/antlr4/imports/sql92/DDLStatement.g4:68-80.
• SQL92DDLStatementVisitor.visitColumnDefinition() now derives notNull from the parsed NOT NULL option at SQL92DDLStatementVisitor.java:115-125.
• Explicit NULL and columns without a nullability option remain notNull=false.
• The parser test covers both boundaries through create_table_with_explicit_column_nullability_sql92:
  • order_id INT NOT NULL
  • user_id INT NULL
• ColumnDefinitionSegmentBinder preserves the metadata through binding.
• Verification on the reviewed head:
  • SQL92 parser module passed.
  • InternalSQL92ParserIT: 208 tests passed.
  • Spotless passed.
  • Checkstyle reported 0 violations.
  • git diff --check passed.

Coverage

• Base: 415e37ead38c6b3e5e39127e23cdf4de47032e11.
• GitHub's authoritative file list matches the local triple-dot scope: 4 files, +14/-2.
• Reviewed RELEASE-NOTES.md, SQL92DDLStatementVisitor.java, the SQL92 supported SQL cases, and the SQL92 expected parser cases.
• Completed root-cause and behavior, blast-radius and contracts, and tests/runtime/operations discovery.
• Checked the SQL92 parser facade, grammar option boundaries, shared binder path, ColumnDefinitionSegment, and the Encrypt CREATE TABLE consumer.
• SQL92 grammar, visitor behavior, parser assertions, release note, and standard references are consistent.
• No unresolved evidence or coverage gap remains; Completion Gate passed.

This is a code-scope review; CI was not reviewed.