util: improve textencoder encodeInto performance #1168

Job	Run time
Build slim tarball	1m 30s
aarch64-linux: with shared libraries	8m 1s
aarch64-darwin: with shared libraries	28m 47s
x86_64-darwin: with shared libraries	58m 39s
x86_64-linux: with shared libraries	10m 55s
	1h 47m 52s

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