LSIF: Code reorganization

Created by: efritz

Some quality of life improvements within the code:

• organize code by entrypoint (server, worker, shared)
• group cohesive files into directories (xrepo + commit, cache + database + backend)
• disambiguate lsp, lsif, and model names via named imports (e.g. RangeId is defined in more than one of these)

This PR only rearranges code, it does not change any implementation. See commits for detailed steps.

Created by: codecov[bot]

Codecov Report

Merging #6511 into master will increase coverage by 0.02%. The diff coverage is 34.4%.

@@            Coverage Diff             @@
##           master    #6511      +/-   ##
==========================================
+ Coverage   39.43%   39.46%   +0.02%     
==========================================
  Files        1195     1213      +18     
  Lines       61605    61592      -13     
  Branches     5856     5851       -5     
==========================================
+ Hits        24295    24308      +13     
+ Misses      35085    35061      -24     
+ Partials     2225     2223       -2

Impacted Files	Coverage Δ
lsif/src/shared/metrics.ts	71.42% <ø> (ø)
lsif/src/worker/importer/input.ts	100% <ø> (ø)
lsif/src/shared/xrepo/bloom-filter.ts	100% <ø> (ø)
lsif/src/shared/datastructures/default-map.ts	100% <ø> (ø)
lsif/src/shared/datastructures/disjoint-set.ts	94.11% <ø> (ø)
lsif/src/shared/database/inserter.ts	94.11% <ø> (ø)
lsif/src/shared/queue/queue.ts	0% <ø> (ø)
lsif/src/shared/xrepo/metrics.ts	100% <ø> (ø)
lsif/src/tests/util.ts	94.44% <ø> (ø)
lsif/src/shared/models/dump.ts	100% <ø> (ø)
... and 74 more