[dev.typeparams] all: merge master (912f0750) into dev.typeparams

Conflicts:

- src/cmd/compile/internal/escape/escape.go

  On master, CL 332230 changed the ">=" in HeapAllocReason to ">"; but
  on dev.typeparams, CL 329989 moved HeapAllocReason into utils.go.

Merge List:

+ 2021-07-02 912f0750 net/http: mention socks5 support in proxy
+ 2021-07-02 287c5e80 cmd/compile: fix stack growing algorithm
+ 2021-07-02 743f03ee spec, unsafe: clarify unsafe.Slice docs
+ 2021-07-02 6125d0c4 cmd/dist: correct comment: SysProcAttri -> SysProcAttr
+ 2021-07-01 03761ede net: don't reject null mx records
+ 2021-07-01 877688c8 testing: add TB.Setenv
+ 2021-07-01 ef8ae82b cmd/compile: fix bug in dwarf-gen var location generation
+ 2021-07-01 770899f7 cmd/go: add a regression test for 'go mod vendor' path traversal
+ 2021-07-01 835d86a1 cmd/go: use path.Dir instead of filepath.Dir for package paths in 'go mod vendor'
+ 2021-07-01 eb437ba9 cmd/compile: make stack value size threshold comparisons consistent
+ 2021-07-01 9d65578b cmd/compile: fix typos in document

Change-Id: I08aa852441af0f070aa32dd2f99b6fa4e9d79cfa