[dev.cmdgo] all: merge master (67f7e16b) into dev.cmdgo

Merge List:

+ 2021-08-27 67f7e16b encoding/gob: optimize decoding of []byte
+ 2021-08-27 2c60a99f cmd/compile/internal/syntax: make valid type parameter list in presence of errors
+ 2021-08-27 d350a665 cmd/compile: eagerly CalcStructSize for synthetic ABI types
+ 2021-08-27 d7e2e2ec cmd/compile: delay fillinMethods to deal with mutually-recursive types
+ 2021-08-27 c9275997 cmd/compile: eliminate repetitive code
+ 2021-08-27 62f88b6d cmd/compile: add types.RecalcSize
+ 2021-08-27 e7eee5e2 cmd/compile: remove ssagen/pgen_test.go
+ 2021-08-27 f153b673 cmd/compile: use typecheck.InitUniverse in unit tests
+ 2021-08-26 967a8017 cmd/compile: move types init code into package types
+ 2021-08-26 af80af22 cmd/compile/internal/types2: do not declare new methods on instantiated types
+ 2021-08-26 03db2c24 cmd/compile/internal/types2: implement TypeList.String (debugging support)
+ 2021-08-26 c9e05fdc cmd/compile: fix reference to generic type needed by crawler
+ 2021-08-26 eb6a07fc cmd/compile: unexport Type.Vargen
+ 2021-08-26 38369837 cmd/compile/internal/types: unexport Type.Extra
+ 2021-08-26 1f8d4562 cmd/compile: change typecheck.iscmp into ir.Op.IsCmp

Change-Id: I95c040a0e984a13a3b12c50458148007221ee300