fix: cordova-fetch with npm@7

[raphinesse]

Motivation and Context

apache/cordova-lib#859

Description

Instead of parsing the installed package's name out of the output of npm install <spec> (which does not work anymore with npm@7) we now do the following:

• First try to determine the name from the spec using npm-package-arg. This is very cheap.
• If that fails, get out the big guns and fetch a full manifest using pacote.

Both of these libraries are also used by npm itself.

Fetching the manifest can be expensive (e.g. for a git repo spec). But since pacote and npm share a cache and we always install a package after fetching a manifest anyway, the additional cost should be negligible in our case. Measuring the execution time of this repo's tests on my machine seems to confirm this: the time is roughly the same before and after this PR.

Furthermore this PR makes some adjustments to test expectations to handle minor behavior changes in npm@7.

Testing

• Included test suite passes for npm@6 and npm@^7.2
• Except for one test, cordova-lib's tests pass when using this branch with npm@^7.2
  (The one that doesn't, is due to npm v7 does not install linked packages dependencies npm/cli#2339 and unrelated to the changes here)

TODO

• Add CI test w/ npm@7
• Report to npm that uninstall seems to be broken with --no-save on npm@7 ([BUG] uninstall does not remove --no-save installed package from node_modules npm/cli#2309)
• Do something about the test that is failing due to [BUG] uninstall does not remove --no-save installed package from node_modules npm/cli#2309 Using fixed npm 7.2 now
• Check if pacote and npm are sharing a cache as expected. The test duration increased from 90s to 110–120s with this change. So we are actually spending a bit more extra time than expected. My latest tests show very similar running times. That's good enough for me.
• Test with cli & lib
• Maybe replace a few of the unit tests I threw out here 👎 🤷‍♂️

[codecov-io]

Codecov Report

Merging #91 (dace3fc) into master (1d96eae) will increase coverage by 0.90%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #91      +/-   ##
==========================================
+ Coverage   92.42%   93.33%   +0.90%     
==========================================
  Files           1        1              
  Lines          66       60       -6     
==========================================
- Hits           61       56       -5     
+ Misses          5        4       -1     

Impacted Files	Coverage Δ
index.js	93.33% <100.00%> (+0.90%)	⬆️

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[breautek]

lgtm