Add `npm run ava` command, update instructions, and exclude files from VSCode search #10441

Job	Run time
analyze-other (actions)	53s
analyze-other (python)	1m 0s
check-codeql-versions	35s
analyze-javascript (windows-2022, linked)	6m 22s
analyze-javascript (ubuntu-22.04)	3m 57s
analyze-javascript (windows-2025)	7m 6s
analyze-javascript (ubuntu-24.04)	4m 6s
analyze-javascript (windows-2022)	6m 26s
analyze-javascript (ubuntu-22.04, linked)	4m 7s
analyze-javascript (macos-13, linked)	8m 55s
analyze-javascript (ubuntu-24.04, linked)	4m 8s
analyze-javascript (macos-14)	6m 21s
analyze-javascript (macos-14, linked)	5m 24s
analyze-javascript (macos-15)	6m 49s
analyze-javascript (macos-15, linked)	8m 44s
analyze-javascript (windows-2025, linked)	5m 49s
analyze-javascript (macos-13)	10m 56s
	1h 31m 38s

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