This PR enables diff-informed mode on queries that select a location other than dataflow source or sink. This entails adding a non-trivial location override that returns the locations that are actually selected.

Prior work includes PRs like#19663,#19759, and#19817. This PR uses the same patch script as those PRs to find candidate queries to convert to diff-enabled. This is the final step in mass-enabling diff-informed queries on all the languages.

Commit-by-commit reviewing is recommended.

• I have split the commits that add/modify tests from the ones that enable/disable diff-informed queries.
• If the commit modifies a .qll file, in the commit message I've included links to the queries that depend on that .qll for easier reviewing.
• Feel free to delegate parts of the review to others who may be more specialized in certain languages.

Potentially tricky cases:

• [TEST] C++: CWE-020/ExternalAPI: add tests based on qlhelp: I wasn't able to get alerts to show up for the qhelp-based tests; can someone from the language team chip in to what a useful test would look like? Similar case with thePython TimingAttackAgainstHash test. In contrast, in[TEST] Java: CWE-020/ExternalAPI I was able to get alerts just from the qhelp example, and in[TEST] C++: CleartextSqliteDatabase I was able to get alerts from a mostly Copilot-written test.