Rust: Exclude skipped files in rust/diagnostic/database-quality

[geoffw0]

Exclude skipped files in rust/diagnostic/database-quality (i.e. the query that powers the tool status page). Skipped files are files skipped by conditional compilation, so they should not affect metrics, and we should not necessarily expect that calls, macros etc in them are actually resolvable anyway.

Unfortunately the overall effect of this change is quite limited, at least on the MRVA-1000 - only one project in that set that had a tool status page warning before does not have one now (previously 132 projects, now 131). Others have slightly better numbers but have not crossed a threshold. There's more to be done on narrowing down the causes of this issue.

[Copilot]

Pull Request Overview

This PR refines database quality statistics by filtering out files that were skipped during compilation, ensuring metrics only reflect actively compiled code.

• Introduces a RelevantFile class to exclude compilation-skipped files from statistics
• Updates all telemetry statistics modules to only count elements from relevant files
• Clarifies the fromSource() documentation to distinguish source files from dependencies

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 1 comment.

File	Description
rust/ql/src/queries/telemetry/DatabaseQuality.qll	Adds RelevantFile filter and applies it to all statistic counts in CallTargetStats, MacroCallTargetStats, and ExprTypeStats modules
rust/ql/lib/codeql/files/FileSystem.qll	Improves documentation for fromSource() predicate to clarify it identifies target project files vs dependencies

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