add a function that we can inspect to jump to the source of a signal, and give every signal a unique id that devtools can use to match signals across calls to getSignalGraph

PR Checklist

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• The commit message follows our guidelines: https://github.com/angular/angular/blob/main/contributing-docs/commit-message-guidelines.md
• Tests for the changes have been added (for bug fixes / features)
• Docs have been added / updated (for bug fixes / features)

PR Type

What kind of change does this PR introduce?

• Bugfix
• Feature
• Code style update (formatting, local variables)
• Refactoring (no functional changes, no api changes)
• Build related changes
• CI related changes
• Documentation content changes
• angular.dev application / infrastructure changes
• Other... Please describe:

What is the current behavior?

Issue Number: N/A

What is the new behavior?

signals are now given a unique ID using a weakmap, and if they have a user function, we pass that through to the caller so they can call inspect(debuggableFn) to get chrome to jump to the source of the signal (see #61540 for usage)

Does this PR introduce a breaking change?

• Yes
• No

Other information