Update explicit control evaluator for agenda and stash visualisation

[dickongwd]

Explicit Control Evaluator Update

Description

This pull request presents incremental updates to the explicit control evaluator for the agenda and stash visualisation on the frontend (link to PR).

Changes

• Source nodes are added to instructions to support editor highlighting
• Step counter has been revised to show the Program node at the start of execution
• Other minor updates to the interpreter's logic

Future Work

• Refactor the codebase to remove suspended states caused by breakpoints. This was mentioned previously in Add Interactive Environment Visualiser #1403.
• Add test suite for the interpreter

[coveralls]

Pull Request Test Coverage Report for Build 5356077226

• 48 of 52 (92.31%) changed or added relevant lines in 6 files are covered.
• 9 unchanged lines in 1 file lost coverage.
• Overall coverage decreased (-0.1%) to 83.476%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
src/ec-evaluator/interpreter.ts	30	31	96.77%
src/ec-evaluator/utils.ts	1	4	25.0%

Files with Coverage Reduction	New Missed Lines	%
src/ec-evaluator/utils.ts	9	81.73%

Totals
Change from base Build 5112940192:	-0.1%
Covered Lines:	10617
Relevant Lines:	12308

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💛 - Coveralls

[martin-henz]

All changes look good to me. The location information is necessary for the line highlighting feature.