Add --built-in-only flag to module migrator #185

Job	Run time
Static analysis	22s
Dart tests \| Dart stable \| ubuntu-latest	57s
Dart tests \| Dart stable \| windows-latest	1m 27s
Node tests \| Dart stable \| Node 18 \| ubuntu-latest	1m 0s
Dart tests \| Dart stable \| macos-latest	1m 2s
Node tests \| Dart stable \| Node 18 \| windows-latest	1m 58s
Node tests \| Dart stable \| Node 18 \| macos-latest	48s
Node tests \| Dart stable \| Node 16 \| ubuntu-latest	1m 9s
Node tests \| Dart stable \| Node 14 \| ubuntu-latest	59s
Node tests \| Dart dev \| Node \| ubuntu-latest	1m 5s
Sanity checks	0s
Deploy Github: Linux	0s
Deploy Pub	0s
Deploy npm	0s
Deploy Homebrew	0s
Deploy Github: Windows	0s
Deploy Github: Mac OS	0s
	10m 47s

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