add monitor callbacks for WriteContent #851

Job	Run time
build-linux (debug, static_lib)	34s
build-darwin (debug, static_lib, x64)	30s
build-linux (debug, shared_lib)	27s
cancel-old-build	3s
build-win32 (debug, static_lib)	1m 4s
build-linux (debug, cmd)	30s
build-darwin (debug, static_lib, arm64)	27s
build-win32 (debug, shared_lib)	1m 10s
build-darwin (debug, shared_lib, x64)	41s
build-linux (release, static_lib)	1m 3s
build-win32 (debug, cmd)	1m 7s
test-darwin (debug, arm64)	1m 10s
build-darwin (debug, shared_lib, arm64)	38s
build-linux (release, shared_lib)	51s
build-win32 (release, static_lib)	1m 45s
test-darwin (debug, x64)	43s
build-darwin (debug, cmd, x64)	39s
build-linux (release, cmd)	49s
build-win32 (release, shared_lib)	1m 51s
build-darwin (debug, cmd, arm64)	53s
test-darwin (release, arm64)	52s
build-win32 (release, cmd)	1m 36s
build-darwin (release, static_lib, x64)	1m 59s
test-darwin (release, x64)	1m 12s
build-darwin (release, static_lib, arm64)	1m 22s
test-linux (debug)	51s
test-linux (release)	56s
build-darwin (release, shared_lib, x64)	1m 41s
test-win32 (debug)	56s
build-darwin (release, shared_lib, arm64)	49s
test-win32 (release)	2m 10s
build-darwin (release, cmd, x64)	1m 19s
build-darwin (release, cmd, arm64)	59s
dist-linux	26s
dist-win32	53s
dist-darwin (x64)	43s
dist-darwin (arm64)	24s
	36m 3s

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