util: improve textencoder encodeInto performance #1200

Job	Run time
Build slim tarball	1m 38s
aarch64-darwin: with shared libraries	30m 16s
aarch64-linux: with shared libraries	7m 59s
x86_64-linux: with shared libraries	10m 45s
x86_64-darwin: with shared libraries	55m 47s
	1h 46m 25s

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