Unexpected 100% CPU usage

[luchsh]

Reported by customer:

• function java.util.base64.decoder.decode occupies huge CPU time
• so far, no jmh or smaller testcase available

[duanyangjing]

jdk8/17 have identical public methods in Base64.java, but jvm17 added new intrinsics like java/util/Base64$Encoder.encodeBlock. Maybe we can try put Base64.java into altkernel.