Improve macro error handling

[devongovett]

This fixes two issues with macro error handling:

1. If you made a syntax error in a macro (or any dev dependency), fixing it would not trigger a rebuild in watch mode. This is because errors thrown by transformers short-circuit adding dev dependencies for plugins in Transformation.js. This is fixed by adding a try...finally around that code.
2. If you have a single macro import that is used multiple times in the same file, it will output the same load error multiple times. Now we distinguish between errors loading the macro file (e.g. resolution + syntax), from execution errors and only show load errors once. The diagnostic also shows the import statement as the location rather than each call.

[mischnic]

There's a failing test on Windows (though introduced before this PR):

  4) macros
       should throw a diagnostic when a macro cannot be resolved:

      AssertionError [ERR_ASSERTION]: Expected values to be loosely deep-equal:

[
  {
    codeFrames: [
      {
        codeHighlights: [
          {
            end: {
              column: 57,
              line: 1
            },
            message: undefined,
            start: {
              column: 1,
              line: 1
            }
          }
        ],
        filePath: 'D:\\a\\parcel\\parcel\\packages\\core\\integration-tests\\test\\macros\\13\\index.js'
      }
    ],
    hints: null,
    message: 'Error loading macro: Could not resolve module "./macro.js" from "D:\\...

should loosely deep-equal

[
  {
    codeFrames: [
      {
        codeHighlights: [
          {
            end: {
              column: 57,
              line: 1
            },
            message: undefined,
            start: {
              column: 1,
              line: 1
            }
          }
        ],
        filePath: 'D:\\a\\parcel\\parcel\\packages\\core\\integration-tests\\test\\macros\\13\\index.js'
      }
    ],
    hints: null,
    message: 'Error loading macro: Could not resolve module "./macro.js" from "D:\\...
      + expected - actual

               "filePath": "D:\\a\\parcel\\parcel\\packages\\core\\integration-tests\\test\\macros\\13\\index.js"
             }
           ]
           "hints": [null]
      -    "message": "Error loading macro: Could not resolve module \"./macro.js\" from \"D:\\\\a\\\\parcel\\\\parcel\\\\packages\\\\core\\\\integration-tests\\\\test\\\\macros\\\\13\\\\index.js\""
      +    "message": "Error loading macro: Could not resolve module \"./macro.js\" from \"D:\\a\\parcel\\parcel\\packages\\core\\integration-tests\\test\\macros\\13\\index.js\""
           "origin": "@parcel/transformer-js"
         }
       ]
      
      at Context.<anonymous> (test\/macros.js:377:14)

[devongovett]

Ah. Windows CI is so flaky I missed it. 😕

Will address separately.