[Test explorer] Improve tree view

[AndreiOrmanji]

Description

Currently test explorer groups only test methods under test files for tree view. It would be nice to group test files as well, to be able to expand/collapse whole folder of temp files, how it is for other test explorer extensions like recca0120.vscode-phpunit extension or JS extension Orta.vscode-jest for such functionality.

Example:

On the screenshot below you can see 3 entries:

1. JS extension Orta.vscode-jest
2. PHP extension recca0120.vscode-phpunit with name PHPUnit
3. DEVSENSE test explorer with name PHPUnit Tests

In my humble opinion, recca0120.vscode-phpunit has better tree view implementation, so it would be nice to have similar functionality in DEVSENSE test explorer, or at least to disable Test Explorer functionality of DEVSENSE extension to be able to use other third-party extensions, like recca0120.vscode-phpunit.

Summary:

List of suggested improvements:

1. Please add posibility to disable TestExplorer functionality of DEVSENSE extension
2. Improve grouping of tests, to be able to group not only test methods, but test files by their location, or even tags