Java: Diff-informed CleartextStorageCookie.ql

[jbj]

I picked this commit out of #17846 because it doesn't rely on any of the controversial API changes that are holding back that PR. It appears there are no tests for CleartextStorageCookie.ql.

This query shares implementation with several other queries about cleartext storage, but it's the only one of them that's in the code-scanning suite. The sharing mechanism remains the same as before, but now each query has to override getASelectedLocation to become diff-informed.

Two other data-flow configurations are used in this query, but they can't easily be made diff-informed.

[Copilot]

Pull Request Overview

Adds diff-informed support to the cleartext storage cookie query by extending the base sink API and implementing location selection for the cookie sink.

• Introduce getASelectedLocation in CleartextStorageSink to enable diff-informed queries.
• Update SensitiveSourceFlowConfig to observe diff-informed mode.
• Implement CookieCleartextStorageSink with unification of the cookie variable and override of getASelectedLocation.

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated no comments.

File	Description
java/ql/lib/semmle/code/java/security/CleartextStorageQuery.qll	Stubbed out getASelectedLocation on base sink and updated flow config
java/ql/lib/semmle/code/java/security/CleartextStorageCookieQuery.qll	Added CookieCleartextStorageSink with diff-informed location override

Comments suppressed due to low confidence (4)

java/ql/lib/semmle/code/java/security/CleartextStorageQuery.qll:14

• [nitpick] Add a doc comment on getASelectedLocation to explain its role in diff-informed mode and that returning none() opts out of diff-informed execution.

  Location getASelectedLocation() { none() }

java/ql/lib/semmle/code/java/security/CleartextStorageCookieQuery.qll:10

• [nitpick] Include a brief comment on the cookie field clarifying that it is bound via pattern unification in the constructor.

  Cookie cookie;

java/ql/lib/semmle/code/java/security/CleartextStorageCookieQuery.qll:14

• [nitpick] Document the selection logic in getASelectedLocation to describe why each location branch is included and how they’re prioritized.

  override Location getASelectedLocation() {

java/ql/lib/semmle/code/java/security/CleartextStorageCookieQuery.qll:9

• There are no tests covering CleartextStorageCookieQuery; consider adding tests to verify diff-informed sink selection and overall query correctness.

private class CookieCleartextStorageSink extends CleartextStorageSink {