Add public API event for kernel post-initialization #17410

Job	Run time
Lint	2m 2s
Build VSIX	1m 16s
cancel_previous_runs	2s
Type Script Tests (ubuntu-latest, ts-unit)	1m 24s
Tests (raw, python, 3.10, ^[^@]+$\|@mandatory\|@kernelCore\|@python\|@jupyter, ubuntu-latest)	6m 53s
Type Script Tests (windows-latest, ts-unit)	6m 4s
Tests (raw, python, 3.10, @widgets, ubuntu-latest)	4m 32s
Tests (raw, python, 3.10, @iw, ubuntu-latest)	4m 14s
Tests (raw, python, 3.10, @webview\|@export\|@lsp\|@variableViewer, ubuntu-latest)	4m 22s
Tests (raw, python, 3.10, @debugger, ubuntu-latest)	3m 49s
Tests (remote, python, 3.10, ^[^@]+$\|@mandatory, ubuntu-latest)	3m 37s
Tests (web, python, 3.10, ^[^@]+$\|@mandatory, ubuntu-latest)	3m 32s
Tests (raw, python, 3.10, ^[^@]+$\|@mandatory, windows-latest)	4m 39s
Tests (raw, python, 3.10, @widgets, ubuntu-latest, 8)	4m 54s
Tests (remote, python, 3.10, @widgets, ubuntu-latest, 8)	5m 59s
Tests (raw, conda, 3.10, ^[^@]+$\|@mandatory\|@python, ubuntu-latest)	4m 22s
Tests (raw, noPython, @nonPython, ubuntu-latest)	1m 45s
Tests (remote, python, 3.10, @kernelCore, ubuntu-latest)	4m 24s
Smoke tests (ubuntu-latest, 3.10)	1m 29s
Smoke tests (windows-latest, 3.10)	3m 32s
Smoke tests (macos-latest, 3.10)	1m 24s
	1h 14m 15s

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