With this change, the static version variable in Leaflet.js will be replaced automatically with the version of package.json everytime npm version is called.

With this solution Firefox versions before May can use the non-bundled code too. They didn't support json import: import pkg from '../package.json' with { type: "json" };

Solved issues with this approach:

• It is possible to use the non-bundled code and we have always included the correct version instead of latest or some other placeholder
• We have a static version instead of importing the version from package.json where the whole file was included. Named export of only the version is not possible.

  See Run test with the source files #9609 (comment). At the moment, the entire content of package.json ends up in the dist bundle.

• We keep the git hash in the banner
• We can remove the karma preprocessor

Looks like this then:

Supersedes #9657, #9662

@simon04 please review too