Use emit_lines instead of bunches of emit_line calls #10661

Job	Run time
Test mypyc suite with 32-bit Python	10m 37s
Test suite with py38-ubuntu, mypyc-compiled	31m 7s
Test suite with py38-windows-64	39m 45s
Test suite with py39-ubuntu	26m 42s
Test suite with py310-ubuntu	20m 24s
Test suite with py311-ubuntu, mypyc-compiled	27m 38s
Test suite with py312-ubuntu, mypyc-compiled	35m 48s
mypyc runtime tests with py38-macos	7m 37s
mypyc runtime tests with py38-debug-build-ubuntu	7m 54s
Type check our own code (py38-ubuntu)	2m 4s
Type check our own code (py38-windows-64)	3m 9s
Formatting and code style with Black + ruff	50s
	3h 33m 35s

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