Option to disable semicolon insertion

When completing certain keywords, rust-analyzer appends a semicolon which is not visible in the preview text. For example:

With return, it is sensible-enough to account for return type, but I still find it intrusive:

• this is actually inconsistent behavior
• it messes with my expectations and muscle memory, since the semicolon is not in the preview text and I am used to typing it manually
• with break and continue, it doesn't consider context; I may want to specify a label, but the semicolon is inserted even when inside of labeled loops, so I have to delete the semicolon in those cases

https://rust-analyzer.github.io/book/configuration.html#completion.addSemicolonToUnit exists, but from a cursory reading of the source code, this only seems to apply to function call snippets which I also have disabled.

Start with the configuration documentation for completion.addSemicolonToUnit, then trace how semicolons are added to return, break, and continue completions. Done means users can disable these keyword insertions independently, including when labels are valid, with tests covering the affected completion cases.