util: improve textencoder encodeInto performance #1137

Job	Run time
Build slim tarball	1m 23s
aarch64-linux: with shared libraries	14m 4s
x86_64-linux: with shared libraries	14m 8s
aarch64-darwin: with shared libraries	14m 20s
x86_64-darwin: with shared libraries	14m 27s
	58m 22s

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