Tracking issue: compiler issues

[nrc]

The next phase of RLS development is probably going to be much more compiler-focussed. This is an issue for tracking stuff from the RLS side. Some areas:

• performance (see Compiler Performance Tracking Issue rust#48547 (comment)) - compiler performance is pretty much the bottleneck for RLS performance
• compiler-driven code completion
• on-demand queries to replace/augment save-analysis data
• keeping track of changes as the AST and other data structures evolve