[dev.cmdgo] all: merge master (5e6a7e9b) into dev.cmdgo

Merge List:

+ 2021-08-26 5e6a7e9b embed: remove reference to global variables in docs
+ 2021-08-26 166b691b cmd/compile/internal/types2: remove need for instance (struct)
+ 2021-08-26 d6bdae33 cmd/compile/internal/types2: address some TODOs (cleanup)
+ 2021-08-26 770df2e1 crypto/tls: fix typo in PreferServerCipherSuites comment
+ 2021-08-26 a6ff433d cmd/go: pass -gcflags after other flags generated by the go command
+ 2021-08-25 4f262028 cmd/compile/internal/types2: fix type set printing and add test
+ 2021-08-25 0ac64f6d cmd/compile/internal/types2: rename IsMethodSet to IsConstraint (cleanup)
+ 2021-08-25 4068fb6c cmd/compile: always accept 1.18 syntax but complain if not 1.18
+ 2021-08-25 bf0bc412 go/types, types2: don't re-evaluate context string for each function argument (optimization)
+ 2021-08-25 4158e88f cmd/compile/internal/syntax: fix position of type parameter field
+ 2021-08-25 647bef6c go/types: implement NewTypeList and use it instead of composite literals
+ 2021-08-25 6cf1d5d0 cmd/compile: generic SSA rules for simplifying 2 and 3 operand integer arithmetic expressions
+ 2021-08-25 5baf60d4 bytes, strings: optimize Trim for single byte cutsets
+ 2021-08-25 3d667671 cmd/compile: fix function contains no TParam in generic function
+ 2021-08-25 4f2ebfe3 cmd/compile: allow embed into any byte slice type
+ 2021-08-25 d2f002cb time/format: avoid growslice in time.String()/time.GoString()
+ 2021-08-25 08d4cc20 cmd/compile: fix stencil call expression.
+ 2021-08-25 099b8190 cmd/compile: fix CheckSize() calculation for -G=3 and stencils
+ 2021-08-25 e1fcf885 test: add test that caused gofrontend compiler crash
+ 2021-08-25 d37b8ded test: add test case that gofrontend miscompiled
+ 2021-08-25 41b99dab os/user: don't skip TestLookupGroup if supported
+ 2021-08-25 de1c934b cmd/compile: fix checkptr false positive for (*[Big]T)(ptr)[:n:n] pattern
+ 2021-08-24 54cdef1f reflect: add MapIter.SetKey and MapIter.SetValue
+ 2021-08-24 5d863f89 cmd/compile: simplify bad conversion check

Change-Id: I29ab927f0e47f44d82f9307c642900f75f4f678f