Convert JS files to TS files core directory part 1

### What is this about?

Convert this JS files to TS files

```
app/core/BackgroundBridge/BackgroundBridge.js
app/core/Permissions/specifications.js
app/core/RPCMethods/index.js
app/core/RPCMethods/wallet_addEthereumChain.js
app/core/RPCMethods/wallet_switchEthereumChain.js
```

### Scenario

_No response_

### Design

_No response_

### Technical Details

_No response_

### Threat Modeling Framework

_No response_

### Acceptance Criteria

_No response_

### Stakeholder review needed before the work gets merged

- [ ] Engineering (needed in most cases)
- [ ] Design
- [ ] Product
- [ ] QA (automation tests are required to pass before merging PRs but not all changes are covered by automation tests - please review if QA is needed beyond automation tests)
- [ ] Security
- [ ] Legal
- [ ] Marketing
- [ ] Management (please specify)
- [ ] Other (please specify)

### References

_No response_

Start by reading the five listed files: app/core/BackgroundBridge/BackgroundBridge.js, app/core/Permissions/specifications.js, and the three files under app/core/RPCMethods. Compare them with existing TypeScript conventions in the repository, convert all five while preserving their behavior, and run the repository's type checks and tests to verify the conversion.

Written by the indexing model from the issue text.