Unify various exec calls #81

I'll cc @cristianoc, @mewhhaha and @john-pangalos (sorry for the ping) on this one.

Currently in the codebase there are 3 ways to call a binary:

• Async exec, with path and argument escaping:

  rescript-vscode/server/src/RescriptEditorSupport.ts

  Line 48 in d1e5411

  exec(command, { cwd: executable.cwd }, function (_error, stdout, _stderr) {

• Async exec, that doesn't escape path but does use the right windows bsb binary:

  rescript-vscode/server/src/utils.ts

  Lines 107 to 114 in d1e5411

  	if (process.platform === "win32") {
  	return childProcess.exec(`${bsbPath}.cmd -w`, {
  	cwd: projectRootPath,
  	});
  	} else {
  	return childProcess.execFile(bsbPath, ["-w"], {
  	cwd: projectRootPath,
  	});

• Sync execFileSync, that might not call the right windows bsc binary:

  rescript-vscode/server/src/utils.ts

  Line 83 in d1e5411

  let result = childProcess.execFileSync(

We should really revisit those and streamline them:

• First one:
  • should be execFile, which avoids needing to escape the command path.
  • should also be sync.
  • should work on windows, if it isn't.
• Second one:
  • should use execFile in the win32 branch too, to avoid needing to escape path. Can't use that for a batch script
• Third one
  • should use the right windows bsc binary, if it isn't (where's the needed .cmd part? Windows fixes #71 (comment)).