## Feature Description

If enabled in the user or repository settings, the local branches pointing to the
parents of the revision targeted by `jj commit` will be advanced to the newly
created commit. Support for `jj new` will be added in a future change.

This behavior can be enabled by default for all branches by setting
the following in the config.toml:

```
[experimental-advance-branches]
enabled-branches = ["glob:*"]
```

Specific branches can also be disabled:
```
[experimental-advance-branches]
enabled-branches = ["glob:*"]
disabled-branches = ["main"]
```

Branches that match a disabled pattern will not be advanced, even if they also
match an enabled pattern.

This implements feature request #2338.

In a future commit these tests will run with both `jj commit` and `jj new` since
both will have the same semantics for advancing the branch pointer.

Parameterizing the tests allows us to run both variants without duplicating the
test bodies. Since the commit IDs are different when `jj describe` + `jj new`
is used instead of `jj commit`, this commit also drops the commit IDs from the
test snapshots. This is fine because the commit IDs are not important for these
tests.

When setting the working copy commit, if a single branch points to a parent of
the working copy and advance-branches is enabled for that branch, set Git HEAD
to the branch instead of detatching at the parent commit.