util: improve textencoder encodeInto performance #1165

Job	Run time
Build slim tarball	1m 36s
x86_64-darwin: with shared libraries	46m 34s
x86_64-linux: with shared libraries	10m 23s
aarch64-linux: with shared libraries	8m 48s
aarch64-darwin: with shared libraries	26m 21s
	1h 33m 42s

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