util: improve textencoder encodeInto performance #1355

Job	Run time
Build slim tarball	1m 30s
x86_64-linux: with shared libraries	30m 3s
x86_64-darwin: with shared libraries	2h 59m 48s
aarch64-linux: with shared libraries	24m 6s
aarch64-darwin: with shared libraries	2h 0m 27s
	5h 55m 54s

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