Stabilize Remappings auto detection

[mattsse]

detecting Remappings is intended to support node_modules as well as dapptools style libraries.

While dapptools' lib folder follows some general rules (directories named lib and src), the average node_modules dependency might not, common patterns are

node_modules/<dep>/lib.sol
node_modules/<dep>/contracts/lib.sol
node_modules/<dep>/{tokens,auth,...}/{contracts, interfaces}/lib.sol
node_modules/<dep>/contracts/{tokens,auth,..}/lib.sol

It's also common that these are nested (especially for dapptools)
lib/ds-token/lib/ds-stop/lib/ds-note/src/contract.sol

Detection needs to be fast (especially for node_modules) and deterministic