Enhancement: RenameVariables transformer

We have a requirement to bulk-replace variables, and wondered if we can leverage Robotidy for this.. Simplified test case shown below, our goal would be to replace the variables `OLD_SCALAR` by `NEW_SCALAR`, `OLD` by `NEW`, `OLD_DICT` by `NEW_DICT`, and also `OLD_DICT_2` by `NEW_DICT_2`, but also its keys `old_key1` by `new_key1`.. Obviously this example could also be achieved through regexp substitution, but we would like to explore if Robotidy could do it "better" and "more robust" than a potentially complex regexp.

Really appreciate you looking into this!

```

*** Test Cases ***
Test
Import Variables ${CURDIR}/vars.yaml
Log Variables
FOR ${var} IN @{OLD}
Log ${var}
END

Should Be True ${OLD_SCALAR}
Should Be True ${OLD}
Should be True ${OLD}[1]
Should be True ${OLD_DICT.a}
Should be True ${OLD_DICT}[a]
Should be True ${OLD_DICT_2.old_key1}
Should be True ${OLD_DICT_2}[old_key1]

Do something with ${OLD}
Do something with ${OLD}[1]
Do something with ${OLD_DICT.a}
Do something with ${OLD_DICT}[a]
Do something with ${OLD_DICT_2.old_key1}
Do something with ${OLD_DICT_2}[old_key1]

*** Keywords ***
Do something with ${var}
Log ${var}

```

vars.yaml content:
```
OLD_SCALAR: 1

OLD:
- 1
- 2
- 3

OLD_DICT:
a: 1
b: 1
c: 1

OLD_DICT_2:
old_key1: 1
old_key2: 2
```

Start with the Robot Framework example in the issue and its vars.yaml content to understand the requested replacement scope. Done should cover the listed scalar, list, dictionary, indexed, dotted-key, bracket-key, and keyword-argument references more robustly than complex regexp substitution.

Written by the indexing model from the issue text.