ctags support
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### Problem to solve
When reviewing code, it will be nice to be able to click through to the definition of methods
### Intended users
Developers
### Further details
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### Proposal
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There are many ways to achieve this, but one way would be to implement support for parsing [ctags](https://en.wikipedia.org/wiki/Ctags)
### Permissions and Security
<!-- What permissions are required to perform the described actions? Are they consistent with the existing permissions as documented for users, groups, and projects as appropriate? Is the proposed behavior consistent between the UI, API, and other access methods (e.g. email replies)? -->
There may be arbitrary code execution implications depending on how Turing complete ctags are.
### Documentation
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### Testing
<!-- What risks does this change pose? How might it affect the quality of the product? What additional test coverage or changes to tests will be needed? Will it require cross-browser testing? See the test engineering process for further help: https://about.gitlab.com/handbook/engineering/quality/test-engineering/ -->
### What does success look like, and how can we measure that?
Projects can have users click on a method name, and GitLab will direct to the line where the method is defined.
### Links / references
issue