util: improve textencoder encodeInto performance #1148

Job	Run time
Build slim tarball	1m 27s
x86_64-darwin: with shared libraries	1m 17s
aarch64-darwin: with shared libraries	1m 5s
aarch64-linux: with shared libraries	1m 11s
x86_64-linux: with shared libraries	1m 15s
	6m 15s

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