## Changes
Add `merge.Override` transform. It allows the override one `dyn.Value`
with another, preserving source locations for parts of the sub-tree
where nothing has changed. This is different from merging, where values
are concatenated.
`OverrideVisitor` is visiting the changes during the override process
and allows to control of what changes are allowed or update the
effective value.
The primary use case is Python code updating bundle configuration.
During override, we update locations only for changed values. This
allows us to keep track of locations where values were initially defined
and used for error reporting. For instance, merging:
```yaml
resources: # location=left.yaml:0
jobs: # location=left.yaml:1
job_0: # location=left.yaml:2
name: "job_0" # location=left.yaml:3
```
with
```yaml
resources: # location=right.yaml:0
jobs: # location=right.yaml:1
job_0: # location=right.yaml:2
name: "job_0" # location=right.yaml:3
description: job 0 # location=right.yaml:4
job_1: # location=right.yaml:5
name: "job_1" # location=right.yaml:5
```
produces
```yaml
resources: # location=left.yaml:0
jobs: # location=left.yaml:1
job_0: # location=left.yaml:2
name: "job_0" # location=left.yaml:3
description: job 0 # location=right.yaml:4
job_1: # location=right.yaml:5
name: "job_1" # location=right.yaml:5
```
## Tests
Unit tests
Gleb Kanterov