Consider EE requirements in EE-Section of ManifestEditor

[HannesWell]

The Execution Environments section in the Manifest Editor is currently empty if a bundle only specifies an EE requirement instead of a dedicated Bundle-RequiredExecutionEnvironment header.
For example for third-party OSGi bundles published to Maven-Central this is quite common.

With this change EE requirements are now considered as well:

The main building block for that is the addition of new method ManifestUtils.getRequiredExecutionEnvironments() in the first commit, that derives the required EEs of an OSGi resource based on its EE requirements. For that it only uses the OSGi resources API and is thus one small step to migrate PDE off the Equinox resolver API.

[github-actions]

Test Results

   291 files  ±0     291 suites  ±0   1h 1m 16s ⏱️ + 6m 38s
 3 580 tests ±0   3 504 ✅ ±0   76 💤 ±0  0 ❌ ±0 
11 037 runs  ±0  10 806 ✅ ±0  231 💤 ±0  0 ❌ ±0 

Results for commit 7151716. ± Comparison against base commit 029c7d7.

♻️ This comment has been updated with latest results.

[HannesWell]

Previously the ExecutionEnvironmentSection just operated on the text in the Manifest. With the current state it requires a resolved target-platform that contains a BundleDescription/osgi.Resource for the Manifest to open. While the latter is present anyways in probably most of the cases I'm not confident it is always the case.
Therefore I think we should continue to operate just on the textual model of the Manifest opened in the editor. A lot of the new logic introduced in ManifestUtils can still be used for that and the changes in PluginInputContextManager would be avoided.