Add `npm run ava` command, update instructions, and exclude files from VSCode search #10439

Job	Run time
analyze-other (python)	57s
check-codeql-versions	36s
analyze-other (actions)	51s
analyze-javascript (ubuntu-22.04)	3m 59s
analyze-javascript (ubuntu-24.04)	4m 2s
analyze-javascript (windows-2025, linked)	5m 59s
analyze-javascript (ubuntu-22.04, linked)	4m 5s
analyze-javascript (windows-2025)	6m 11s
analyze-javascript (ubuntu-24.04, linked)	3m 59s
analyze-javascript (windows-2022)	6m 36s
analyze-javascript (windows-2022, linked)	6m 7s
analyze-javascript (macos-13, linked)	7m 19s
analyze-javascript (macos-13)	9m 9s
analyze-javascript (macos-15, linked)	7m 45s
analyze-javascript (macos-15)	7m 14s
analyze-javascript (macos-14, linked)	9m 8s
analyze-javascript (macos-14)	7m 31s
	1h 31m 28s

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