all: REVERSE MERGE dev.cmdgo (220bc44a) into master

This commit is a REVERSE MERGE.
It merges dev.cmdgo back into its parent branch, master.
This marks the end of development on dev.cmdgo.

Merge List:

+ 2021-08-27 220bc44a [dev.cmdgo] all: merge master (67f7e16b) into dev.cmdgo
+ 2021-08-26 de83ef67 [dev.cmdgo] all: merge master (5e6a7e9b) into dev.cmdgo
+ 2021-08-25 de23549a [dev.cmdgo] cmd/go: fix calls to modFileGoVersion to pass in modFile
+ 2021-08-25 3b523caf [dev.cmdgo] cmd/go: clean up TODOWorkspaces instances
+ 2021-08-25 109c13b6 [dev.cmdgo] all: merge master (c2f96e68) into dev.cmdgo
+ 2021-08-12 e2e1987b [dev.cmdgo] cmd/link: fix TestBuildForTvOS
+ 2021-08-12 d397fc11 [dev.cmdgo] don't give command-line-arguments a module
+ 2021-08-11 aaf914d0 [dev.cmdgo] cmd/go: remove modload.ModRoot function
+ 2021-08-06 3025ce2f [dev.cmdgo] cmd/go: address code review comments in test cgo_path_space_quote
+ 2021-08-06 fc8e0cbb [dev.cmdgo] cmd: update x/tools and remove copy of txtar
+ 2021-07-31 37990129 [dev.cmdgo] cmd/go: add go mod editwork command
+ 2021-07-30 b3b53e1d [dev.cmdgo] cmd/go: thread through modroots providing replacements
+ 2021-07-30 47694b59 [dev.cmdgo] cmd/go: provide a more helpful missing required module error in workspaces
+ 2021-07-30 90830699 [dev.cmdgo] cmd/go: allow expliticly setting -mod=readonly in workspace mode
+ 2021-07-30 8e2ab05d Merge "[dev.cmdgo] all: merge master (9eee0ed4) into dev.cmdgo" into dev.cmdgo
+ 2021-07-30 52e970b1 [dev.cmdgo] cmd: support space and quotes in CC and CXX
+ 2021-07-30 3a69cef6 [dev.cmdgo] cmd/internal/str: add utilities for quoting and splitting args
+ 2021-07-30 137089ff [dev.cmdgo] cmd/internal/str: move package from cmd/go/internal/str
+ 2021-07-28 47cdfa95 [dev.cmdgo] all: merge master (9eee0ed4) into dev.cmdgo
+ 2021-07-28 176baafd [dev.cmdgo] cmd/go: sort roots when joining multiple main module roots
+ 2021-07-28 288a83dc [dev.cmdgo] cmd/go: maintain a go.work.sum file
+ 2021-07-27 2c8acf63 [dev.cmdgo] cmd/go: make fewer 'go mod' commands update go.mod
+ 2021-07-27 72233d27 [dev.cmdgo] cmd/go: add -testsum flag to update go.sum in script tests
+ 2021-07-27 b2205eab [dev.cmdgo] cmd/go: add go mod initwork command
+ 2021-07-27 f05f5cef [dev.cmdgo] cmd/go: fold index and modFile into MainModules
+ 2021-07-26 7ce25714 [dev.cmdgo] cmd/go: add the workspace mode
+ 2021-07-26 3cd15e02 [dev.cmdgo] cmd: pull in x/mod on the dev.cmdgo branch
+ 2021-07-22 a627fcd3 [dev.cmdgo] cmd/go: replace Target with MainModules, allowing for multiple targets
+ 2021-07-20 ab361499 [dev.cmdgo] cmd/go/testdata/script: fix a small typo in modfile_flag
+ 2021-07-06 aa4da4f1 [dev.cmdgo] all: merge master (912f0750) into dev.cmdgo
+ 2020-12-22 6dc2c16f [dev.cmdgo] codereview.cfg: add config for dev.cmdgo

Change-Id: Ic42f1273e42c90954bd61a6e4d6ca193c97bf04c