Tracking issue for unstable option: imports_granularity.

Option documentation.

See Processes.md, "Stabilising an Option":

• Is the default value correct?
• The design and implementation of the option are sound and clean.
• The option is well tested, both in unit tests and, optimally, in real usage.
• There is no open bug about the option that prevents its use.
  • Import sorting does not handle uppercase/lowercase consistently #5269
  • fix(import_granularity): do not merge aliases #6028
  • bug: imports_granularity = "One" deletes aliases #6027
  • imports_granularity=Item removes #[cfg()] attribute from imports #5030
  • imports_granularity = "Module" causes compile error when path contains self #4681
  • fix: imports_granularity module with path containing self #5253
  • import_granularity: Don't normalize imports with comments #5311
  • Backport 4406 + 4536 #5296
  • Formatting pre and post cast comments enhancements #4406
  • fix: between span derivation on cast exprs #4536
  • Rustfmt removes comments in uses #3984
  • Do not remove comment from an import with a single item #3999