Implement Vector128 version of System.Buffers.Text.Base64 DecodeFromUtf8 and EncodeToUtf8 (#70654)
* Implement Vector128 version of System.Buffers.Text.Base64.DecodeFromUtf8
Rework the SS3 into a Vector128 version, and add Arm64 support.
* SSE3 improvements
* Remove superfluous bitwise And
* Add comment to SimdShuffle
* Inline SimdShuffle
* Implement Vector128 version of System.Buffers.Text.Base64.EncodeToUtf8
* Ensure masking on SSE3
Change-Id: I319f94cfc51d0542ae4eb11a8d48b3eb8180553f
CustomizedGitHooks: yes
* Restore asserts and move zero inside the loop
* Neater C# code
Change-Id: I2cbe14f4228f8035e7d213b5b58815c4eee35563
CustomizedGitHooks: yes
* Make SimdShuffle consistent across X64 and Arm64
* Better looking multiply