all: REVERSE MERGE dev.simd (b566743) into master

This commit is a REVERSE MERGE.
It merges dev.simd back into its parent branch, master, for 1.27.

Merge List:

+ 2026-05-29 b56674396e [dev.simd] all: merge master (388e94d) into dev.simd
+ 2026-05-29 c59ae5c5a7 [dev.simd] internal/buildcfg: disable simd experiment for reverse merge
+ 2026-05-29 b7b03d9e3d [dev.simd] simd: add arm64 Neon support to midway
+ 2026-05-29 d7b3da6e25 [dev.simd] simd: improve arm64 and amd64 rotateAll
+ 2026-05-29 555dd4691a [dev.simd] simd: add ARM64 NEON MulAdd support
+ 2026-05-29 f1aa77c984 [dev.simd] cmd/compile: first semi-working "midway" translator
+ 2026-05-28 bc1da486f8 [dev.simd] simd: refactor big template in gen_simdTypes into map
+ 2026-05-28 593e8bf9b1 [dev.simd] simd: refactor intrinsics definition
+ 2026-05-28 0442e04934 [dev.simd] simd: refactor rule generation template
+ 2026-05-28 82489f7402 [dev.simd] simd: add insert_ordered_map
+ 2026-05-28 edbc93f594 [dev.simd] simd: add amd64 emulation for FP SIMD negation
+ 2026-05-28 cedf3d5870 [dev.simd] simd: wasm, emulate unsigned OnesCount at all sizes
+ 2026-05-28 d494f566fb [dev.simd] simd, cmd/compile: mul-widening WASM ops are commutative
+ 2026-05-28 a78a574c08 [dev.simd] go/types, cmd/compile: exclude simd/.../sgutil from TestStdlib
+ 2026-05-27 0e68595b42 [dev.simd] simd: fix doc comments in slicepart_128.go
+ 2026-05-27 ecc340ee9c [dev.simd] simd: fix arm64 test build for TruncTo and uint64 shifts
+ 2026-05-26 10231ce696 [dev.simd] simd: add some emulations to amd64
+ 2026-05-26 40eb69725e [dev.simd] simd: add some emulated methods to wasm
+ 2026-05-26 9c6b9b2ece [dev.simd] simd: for wasm, add MulWiden{Lo,Hi}
+ 2026-05-26 fed139a1b3 [dev.simd] simd, cmd/compile: make all shift and rotate take uint64.
+ 2026-05-26 fda1299caf [dev.simd] cmd/compile: add html formatter for "syntax" version of IR
+ 2026-05-26 44a4be991f Revert "[dev.simd] internal/buildcfg: disable SIMD experiment by default for merge to master"
+ 2026-05-26 3e04a409d1 [dev.simd] simd, cmd/compile: TruncateToX -> TruncToX
+ 2026-05-26 8583ef15c8 [dev.simd] simd, cmd/compile: SumAbsDiff -> SumOf8AbsDiff
+ 2026-05-26 35ea327859 [dev.simd] simd, cmd/compile: AddSub->AddOddSubEven, MulAddSub->MulAddOddSubEven

Change-Id: Ib8ed4f0fcaad1074dd5e0c6f4e88c3b7ac896327