fix: backslash at end of string literal was misinterpreted

[olavloite]

SQL strings that contained a string literal with a backslash as the last character were misinterpreted by the statement parser as containing unclosed string literals.

Fixes googleapis/java-spanner-jdbc#2303

[gemini-code-assist]

Summary of Changes

Hello @olavloite, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request addresses a critical parsing bug in SQL statement processing. Previously, string literals that concluded with an escaped backslash were erroneously flagged as unclosed, causing parsing failures. The changes ensure that the parser correctly handles these escape sequences, improving the robustness of SQL statement interpretation.

Highlights

• Bug Fix: SQL String Literal Parsing: Resolved an issue where SQL statement parsing incorrectly identified string literals ending with a backslash as unclosed, leading to parsing errors.
• Enhanced Backslash Escape Handling: The AbstractStatementParser now correctly interprets escaped backslashes (\\) within string literals, preventing misinterpretation of string boundaries.
• New Test Cases: Added new unit tests to SpannerStatementParserTest and StatementParserTest to specifically validate the correct parsing of string literals containing escaped backslashes.

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[gemini-code-assist]

Code Review

This pull request correctly fixes an issue where a backslash at the end of a string literal was misinterpreted by the statement parser. The change in AbstractStatementParser.java to also handle escaped backslashes (\\) is the correct approach. The new test in StatementParserTest.java validates this fix well. However, the test added in SpannerStatementParserTest.java appears to be incorrect and does not test the scenario that was fixed. See the detailed comment for a suggested correction.