FileService's copy/move should not modify the target URI when destination exist

[kittaakos]

Bug Description:

From here:

The FileService API should not change the target URI when moving/copying. Imagine you have a Node.js call:

fs.copyFile('/path/to/my/file', '/path/to/desired/destination', cb)

And eventually, it will copy my file to /path/to/desired/destination_copy just because /path/to/desired/destination already exists. No, the FileService should fail and not modify the destination.

Related: #9037

The current code modifies the target URI if !overwrite . !overwrite has the same meaning as COPYFILE_EXCL from Node. Node fails with EEXIST. I would expect a failure too. Thoughts?

theia/packages/filesystem/src/browser/file-service.ts

Lines 1121 to 1125 in b972e2b

	if (exists && !overwrite) {
	const parent = await this.resolve(target.parent);
	const name = target.path.name + '_copy';
	target = FileSystemUtils.generateUniqueResourceURI(target.parent, parent, name, target.path.ext);
	}

Steps to Reproduce:

Additional Information

• Operating System:
• Theia Version: