[release-branch.go1.16] all: merge master into release-branch.go1.16

1004a7cb runtime/metrics: update documentation to current interface
6530f261 doc/go1.16: remove draft notice
353e1114 doc/go1.16: fix mismatched id attribute
f0d23c9d internal/poll: netpollcheckerr before sendfile
0cb34151 doc: remove all docs not tied to distribution
626ef081 doc: remove install.html and install-source.html
30641e36 internal/poll: if copy_file_range returns 0, assume it failed
33d72fd4 doc/faq: update generics entry to reflect accepted proposal
852ce7c2 cmd/go: provide a more helpful suggestion for "go vet -?"
66c27093 cmd/link: fix typo in link_test.go
ff0e93ea doc/go1.16: note that package path elements beginning with '.' are disallowed
249da7ec CONTRIBUTORS: update for the Go 1.16 release
864d4f1c cmd/go: multiple small 'go help' fixes
26ceae85 spec: More precise wording in section on function calls.
930c2c9a cmd/go: reject embedded files that can't be packed into modules
e5b08e6d io/fs: allow backslash in ValidPath, reject in os.DirFS.Open
ed807909 cmd/compile: mark concrete call of reflect.(*rtype).Method as REFLECTMETHOD
e9c96835 cmd/go: suppress errors from 'go get -d' for packages that only conditionally exist
e0ac989c archive/tar: detect out of bounds accesses in PAX records resulting from padded lengths
c9d6f45f runtime/metrics: fix a couple of documentation typpos
cea4e21b io/fs: backslash is always a glob meta character
dc725bfb doc/go1.16: mention new vet check for asn1.Unmarshal
19018530 runtime/metrics: fix panic in readingAllMetric example
ed3e4afa syscall/plan9: remove spooky fd action at a distance
724d0720 doc/go1.16: add missed heading tag in vet section
b54cd94d embed, io/fs: clarify that leading and trailing slashes are disallowed
4516afeb testing/fstest: avoid symlink-induced failures in tester
8869086d runtime: fix typo in histogram.go
e491c6ee math/big: fix comment in divRecursiveStep
fca94ab3 spec: improve the example in Type assertions section
98f8454a cmd/link: don't decode type symbol in shared library in deadcode
1426a571 cmd/link: fix off-by-1 error in findShlibSection
32e789f4 test: fix incorrectly laid out instructions in issue11656.go
0b6cfea6 doc/go1.16: document that on OpenBSD syscalls are now made through libc
26e29aa1 cmd/link: disable TestPIESize if CGO isn't enabled
6ac91e46 doc/go1.16: minor markup fixes
44361140 embed: update docs for proposal tweaks
68058edc runtime: document pointer write atomicity for memclrNoHeapPointers
c8bd8010 syscall: generate readlen/writelen for openbsd libc
41bb49b8 cmd/go: revert TestScript/build_trimpath to use ioutil.ReadFile
725a642c runtime: correct syscall10/syscall10X on openbsd/amd64
4b068caf doc/go1.16: document go/build/constraint package
376518d7 runtime,syscall: convert syscall on openbsd/arm64 to libc

Change-Id: Icfe3d849f459eda48d7d786d0cd7b082c9c2c325