Cache range and position

[TwitchBronBron]

Cache the range and position objects since they're immutable. This helps reduce memory footprint and garbage collection churn. Also after a range has been created at least once, it should theoretically cost less CPU cycles since we just look it up from the cache instead of building a new one.

For a large private project:

location cache: DISABLED 
build: (8s191.958ms) (7s967.413ms) (8s222.454ms) (8s035.043ms) | (avg: 8.104217seconds)
watch: (8s103.313ms) (8s104.476ms) (8s200.875ms) (8s100.466ms) | (avg: 8.127283seconds)

location cache: ENABLED
build:  (7s965.510ms) (7s977.796ms) (8s167.780ms) (7s960.608ms) (avg: 7.7679235seconds)
watch:  (7s873.529ms) (7s967.520ms) (8s018.557ms) (8s091.832ms) (avg: 7.9878595seconds)

For the same project, we end up caching a ton of ranges and positions. As the app lives in watch mode for a while, I would expect more and more of those locations to get recycled:

cold boot:
Ranges:    254,551 cached 193,085 not cached
Positions: 418,227 cached   10,588 not cached

after 4 watch validations:
Ranges:    392,111 cached 163,335 not cached
Positions: 418,227 cached  10,588 not cached