Investigate / add .gpr support

[itsacoderepo]

As discussed on discord, try to add support for .gpr files.

Snippet from discord (https://discord.com/channels/832209896089976854/832209896089976857/876924134351839243)

  try {
      projectManager = Some(new HeadlessGhidraProjectManager)

      if (inputFile.endsWith(".gpr")) {
        var projname = inputFile.substring(inputFile.lastIndexOf('/')+1, inputFile.lastIndexOf('.'))
        var projdir = inputFile.substring(0, inputFile.lastIndexOf('/'))
        println(s"Found existing Ghidra repo. Loading project $projname from $projdir")
        locator          = new ProjectLocator(projdir, projname)
        project = Some(projectManager.get.openProject(locator, true, true))