refactor(postgresql): remove non-standard builtin_function_name tokens

Align with PostgreSQL's official grammar and ANTLR community standard by
removing built-in function name tokens from the lexer. These function names
(exp, div, floor, mod, power, sqrt, log, etc.) are now properly treated as
regular identifiers, matching PostgreSQL's behavior.

Changes:
- Remove ~475 built-in function tokens from PostgreSQLLexer.g4
  (ABS, CBRT, CEIL, EXP, DIV, FLOOR, MOD, POWER, SQRT, etc.)
- Remove builtin_function_name parser rule from PostgreSQLParser.g4
- Update parser rules: param_name, func_type, generictype, func_name
- Add LOG to plsql_unreserved_keyword (was missing, caused test failures)
- Add .vscode/ to .gitignore

Benefits:
- Matches PostgreSQL's official grammar behavior
- Aligns with ANTLR grammars-v4 community standard
- Simpler, more maintainable grammar
- Function names can naturally be used as identifiers

Test Results:
- All target tests pass: exp, div, floor, mod, power, sqrt, log
- No new regressions in full test suite

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

Author: h3n4l

.gitignore

@@ -47,4 +47,4 @@ go.work.sum
 **/*.class
 
 # No binary files
-**/bin/**
+**/bin/**.vscode/

postgresql/PostgreSQLKeywords.g4

@@ -4,7 +4,7 @@
 //
 // Source: PostgreSQL REL_18_STABLE kwlist.h
 // URL: https://raw.githubusercontent.com/postgres/postgres/REL_18_STABLE/src/include/parser/kwlist.h
-// Generated: 2025-11-13T15:59:19+08:00
+// Generated: 2025-11-13T16:51:25+08:00
 //
 // DO NOT EDIT MANUALLY - This file is generated by keyword-generator
 // To regenerate: cd postgresql && make generate-keywords