Use source files as well to generate mappings

[dmail]

Summary of changes:

• Autogenerate mappings for import without extension: Read main file and imported files recursively to find extensionless import and generate the mappings.
• Update conditions resolution in package exports field to match Node.js behaviour
• Rename getImportMapFromNodeModules -> getImportMapFromProjectFiles
• Rename generateImportMapForProject -> writeImportMapFile
• Add new param: dev
• Add new param: runtime
• Add support for importmap field in package.json (can be an object or string leading to a file)
• Remove param projectPackageDevDependenciesIncluded (replaced by dev)
• Remove param packageExportsPreference (replaced by dev + runtime)
• Remove support for imports field in package.json (now it is ignored)
• Add new param removeUnusedMappings (remove mappings generated from package.json files but not actually used in the codebase)
• Add new param moduleFormat (no need to document this one, I doubt it will ever be useful to someone)
• Updated documentation

There is many breaking changes, so next version is a major.

[codecov[bot]]

Codecov Report

Merging #27 (c4a73f2) into master (413b6aa) will increase coverage by 4.86%. The diff coverage is 79.19%.