Naming strategy UnderScoreSeparatedLowerCase does not work with two Upper characters after each other

### Task List

- [x] Steps to reproduce provided
- [] Stacktrace (if present) provided
- [] Example that reproduces the problem uploaded to Github
- [x] Full description of the issue provided (see below)

### Steps to Reproduce

1. Call io.micronaut.core.naming.NameUtils.separateCamelCase("DataCJpa", false, '_')

### Expected Behaviour

should return 'Data_C_Jpa'

### Actual Behaviour

returns 'Data_CJpa'

### Environment Information

- **Operating System**: Windows 10
- **Micronaut Version:** 2.1.0
- **JDK Version:** 11.0.8

### Example Application

N/A

### How to fix

In class io.micronaut.core.naming.NameUtils in method separateCamelCase on line 370:

change line:
if (Character.isUpperCase(c) && !Character.isUpperCase(last)) {

to:
if (Character.isUpperCase(c)) {

Start in io.micronaut.core.naming.NameUtils, specifically separateCamelCase, and reproduce the issue with NameUtils.separateCamelCase("DataCJpa", false, '_'). Done means the result is 'Data_C_Jpa' rather than 'Data_CJpa'; the issue does not name a test file to run.

Written by the indexing model from the issue text.