Go: improve accuracy of overlay annotations

[owen-mc]

FuncDef.getACall() should be overlay[global]. This reduces the number of alerts that we miss in overlay mode.

I did 4 DCA runs, but only runs 3 and 4 need to be considered.

1. Run 1 failed because of a latent performance issue, fixed in Go: refactor EncryptionOperation #21745.
2. Run 2 was on a subset of one of the standard source suites, and therefore is not directly comparable with previous runs.
3. Run 3 was on the source suite aimed at checking that we do not lose two many results. It shows that we now only have 2 missing results, which is an improvement on the 9 missing results previously. (Side note: the 2 results are not a subset of the previous 9, which I do not understand.)
4. Run 4 was on the source suite aimed at testing performance. This showed a 31% reduction in analysis time. However, this is source suite is full of sources that take a very long time. The source suite used for run 3 contains mostly small repos, which are more representative. The reduction in analysis time in run 3 was 14%.

[Copilot]

Pull request overview

This PR updates Go QL library overlays and crypto modeling to improve annotation accuracy and make encryption-operation modeling use explicit flow-target accessors.

Changes:

• Refactors Cryptography::EncryptionOperation to require getEncryptionFlowTarget() and updates subclasses accordingly.
• Adjusts overlay annotations (for example overlay[local?] and overlay[global]) on selected Go library modules/members to improve overlay behavior.
• Updates crypto/cipher StreamReader/StreamWriter models to provide explicit encryption-target and input nodes via overrides.

Show a summary per file

File	Description
go/ql/lib/semmle/go/frameworks/CryptoLibraries.qll	Updates crypto/cipher stream operation models to override the new encryption flow target accessor and provide inputs explicitly.
go/ql/lib/semmle/go/dataflow/internal/DataFlowNodes.qll	Tweaks overlay annotations and marks selected call-target resolution helpers as overlay[global].
go/ql/lib/semmle/go/Scopes.qll	Updates module overlay annotation and marks Function.getACall() as overlay[global].
go/ql/lib/semmle/go/Decls.qll	Updates module overlay annotation and marks FuncDef.getACall() as overlay[global].
go/ql/lib/semmle/go/Concepts.qll	Refactors EncryptionOperation to use an abstract getEncryptionFlowTarget() and updates EncryptionMethodCall accordingly.

Copilot's findings

• Files reviewed: 5/5 changed files
• Comments generated: 0

[aschackmull]

LGTM