Emit, source map, and declaration cache in deno dir is racy across multiple processes

[dsherret]

I've run into two caching issues while using deno the past two days where I was sure my code was ok, but I was getting type checking errors.

Upon closer inspection, our cache code is racy across multiple processes since the hash is stored in a separate file.

Also, looks like if you kill the process between these two statements then the emit won't be saved correctly and won't ever be reloaded until you change the source text:

deno/cli/emit.rs

Lines 458 to 459 in 12423e1

	cache.set(CacheType::Version, &specifier, version)?;
	cache.set(CacheType::Emit, &specifier, emit.data)?;

To solve this, we should store both the version hash along with each artifact in the same file. I've already started working on a fix. Edit: ended up storing an emit hash in the version file.