Some device paths contain commas outside of groups (i.e. {a,b}) or
classes (i.e. [,.:;'"]).  For example, `/dev/foo,bar` is a valid device
path which one might with to use with the custom-device interface.

Most filesystems allow commas in filepaths, as does apparmor:
https://gitlab.com/apparmor/apparmor/-/blob/master/parser/parser_regex.c#L340

Previously, createRegex() would throw an error if a comma was used
outside of a group or class.  This commit removes that error and instead
treats commas outside of groups and classes as literal commas.  The
accompanying tests are also adjusted to reflect this change.

Signed-off-by: Oliver Calder <oliver.calder@canonical.com>

Rather than allowing any caller of `NewPathPattern()` to successfully
validate paths containing commas, this change adds a boolean argument
which explicitly specifies whether commas should be allowed in the
filepath.

There are some risks involved with allowing commas in filepaths (see
discussion at snapcore#12697), so it is
desirable to restrict when commas are allowed based on the caller.  In
particular, superprivileged interfaces (such as `custom-device` and
`mount-control`) have valid needs for commas in filepaths, and users of
these interfaces are individually verified, so it is safe for them to
use `NewPathPattern()` with commas allowed.  Other callers (particularly
unprivileged interfaces) should probably not allow commas.

I was unsure whether `overlord/hookstate/ctlcmd/mount.go` should call
`NewPathPattern()` with commas allowed or not, but since commas had
previously been disallowed and tests continue to pass with
`allowCommas=false`, then I decided to leave it as `false`.

Signed-off-by: Oliver Calder <oliver.calder@canonical.com>

Also, switched `overlord/hookstate/ctlcmd/mount.go` to allow commas
(previously did not, but this should match what is allowed in
`interfaces/builtin/mount_control.go`.

Signed-off-by: Oliver Calder <oliver.calder@canonical.com>

Signed-off-by: Oliver Calder <oliver.calder@canonical.com>

Since `,` is not a regex special character, the `QuoteMeta` call is
unnecessary.

Signed-off-by: Oliver Calder <oliver.calder@canonical.com>

Signed-off-by: Oliver Calder <oliver.calder@canonical.com>

…=true

Signed-off-by: Oliver Calder <oliver.calder@canonical.com>