perf(cache): single cache file for remote modules

[dsherret]

This changes the global cache to store the cache file for remote modules in one file instead of two.

1. This is better performance as we now do one open file and read instead of two. This will be faster for loading from the deno dir on a network drive or slow storage devices.
2. This makes the cache more resilient because the two files can't get out of sync (or one of them deleted and not the other one, which was previously the source of bugs).
3. This has the downside of making the global cache more complicated, but I think it's worth it. (Edit: not that complicated anymore) Proposed format of the file is outlined in perf: single cache file deno_cache_dir#54

On an m2 macbook loading 10k remote modules:

Benchmark 1: ./deno_main run main.ts
  Time (mean ± σ):      1.143 s ±  0.019 s    [User: 1.061 s, System: 0.560 s]
  Range (min … max):    1.101 s …  1.165 s    10 runs
 
Benchmark 2: ./deno_new run main.ts
  Time (mean ± σ):      1.004 s ±  0.011 s    [User: 1.053 s, System: 0.428 s]
  Range (min … max):    0.983 s …  1.022 s    10 runs
 
Summary
  ./deno_new run main.ts ran
    1.14 ± 0.02 times faster than ./deno_main run main.ts

Closes #17707

[dsherret]

Deleted this test because it's not possible for the two files to get out of sync because there's only one file now.

[bartlomieju]

LGTM, this is indeed much simpler