remove buildkit as dependency

This copies the github.com/moby/buildkit/util/appcontext
package as an internal package. The appcontext package from
BuildKit was the only remaining dependency on BuildKit, and
while we may need some of its functionality, the implementation
is not correct for how it's used in docker/cli (so would need
a rewrite).

Moving a copy of the code into the docker/cli (but as internal
package to prevent others from depending on it) is a first step
in that process, and removes the circular dependency between
BuildKit and the CLi.

We are only using these:

    tree vendor/github.com/moby/buildkit
    vendor/github.com/moby/buildkit
    ├── AUTHORS
    ├── LICENSE
    └── util
        └── appcontext
            ├── appcontext.go
            ├── appcontext_unix.go
            ├── appcontext_windows.go
            └── register.go

    3 directories, 6 files

Before this:

    go mod graph | grep ' github.com/docker/cli'
    github.com/moby/buildkit@v0.11.6 github.com/docker/cli@v23.0.0-rc.1+incompatible

After this:

    go mod graph | grep ' github.com/docker/cli'
    # (nothing)

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

cmd/docker/docker.go

@@ -13,8 +13,8 @@ import (
 	"github.com/docker/cli/cli/command/commands"
 	cliflags "github.com/docker/cli/cli/flags"
 	"github.com/docker/cli/cli/version"
+	"github.com/docker/cli/cmd/docker/internal/appcontext"
 	"github.com/docker/docker/api/types/versions"
-	"github.com/moby/buildkit/util/appcontext"
 	"github.com/pkg/errors"
 	"github.com/sirupsen/logrus"
 	"github.com/spf13/cobra"

vendor/github.com/moby/buildkit/util/appcontext/appcontext.go → cmd/docker/internal/appcontext/appcontext.go

@@ -9,8 +9,10 @@ import (
 	"github.com/sirupsen/logrus"
 )
 
-var appContextCache context.Context
-var appContextOnce sync.Once
+var (
+	appContextCache context.Context
+	appContextOnce  sync.Once
+)
 
 // Context returns a static context that reacts to termination signals of the
 // running process. Useful in CLI tools.

vendor.mod

@@ -23,7 +23,6 @@ require (
 	github.com/google/shlex v0.0.0-20191202100458-e7afc7fbc510
 	github.com/mattn/go-runewidth v0.0.14
 	github.com/mitchellh/mapstructure v1.3.2
-	github.com/moby/buildkit v0.11.6
 	github.com/moby/patternmatcher v0.6.0
 	github.com/moby/swarmkit/v2 v2.0.0-20230713153928-bc71908479e5
 	github.com/moby/sys/sequential v0.5.0

vendor.sum

@@ -164,8 +164,6 @@ github.com/miekg/pkcs11 v1.1.1/go.mod h1:XsNlhZGX73bx86s2hdc/FuaLm2CPZJemRLMA+WT
 github.com/mitchellh/mapstructure v1.0.0/go.mod h1:FVVH3fgwuzCH5S8UJGiWEs2h04kUh9fWfEaFds41c1Y=
 github.com/mitchellh/mapstructure v1.3.2 h1:mRS76wmkOn3KkKAyXDu42V+6ebnXWIztFSYGN7GeoRg=
 github.com/mitchellh/mapstructure v1.3.2/go.mod h1:bFUtVrKA4DC2yAKiSyO/QUcy7e+RRV2QTWOzhPopBRo=
-github.com/moby/buildkit v0.11.6 h1:VYNdoKk5TVxN7k4RvZgdeM4GOyRvIi4Z8MXOY7xvyUs=
-github.com/moby/buildkit v0.11.6/go.mod h1:GCqKfHhz+pddzfgaR7WmHVEE3nKKZMMDPpK8mh3ZLv4=
 github.com/moby/patternmatcher v0.6.0 h1:GmP9lR19aU5GqSSFko+5pRqHi+Ohk1O69aFiKkVGiPk=
 github.com/moby/patternmatcher v0.6.0/go.mod h1:hDPoyOpDY7OrrMDLaYoY3hf52gNCR/YOUYxkhApJIxc=
 github.com/moby/swarmkit/v2 v2.0.0-20230713153928-bc71908479e5 h1:o6x+wIX1vKD0kJlEqe8M9TLIe0SK8lnGcA6XoJtaFqg=

vendor/modules.txt

@@ -182,9 +182,6 @@ github.com/miekg/pkcs11
 # github.com/mitchellh/mapstructure v1.3.2
 ## explicit; go 1.14
 github.com/mitchellh/mapstructure
-# github.com/moby/buildkit v0.11.6
-## explicit; go 1.18
-github.com/moby/buildkit/util/appcontext
 # github.com/moby/patternmatcher v0.6.0
 ## explicit; go 1.19
 github.com/moby/patternmatcher