Use read action to access documents #850

[ArsenHD]

Description

I could not reproduce issue #850, but it seems like the exception occurs because the read lock is not acquired. In this MR I add the read lock acquisition for accessing the Document instances.

Type of Change

• Bug fix (non-breaking change which fixes an issue)

How Has This Been Tested?

Manual Scenario

It is important that after this change util class generation still functions normally. I manually checked how it works in different possible cases.

• org.utbot.examples.structures.StandardStructures (without mocks) - util class with no mock support is generated
• org.utbot.examples.mock.CommonMocksExample (mock strategy: mock class environment) - util class generated at previous step is updated to support mocks
• generated tests on org.utbot.examples.objects.AnonymousClassesExample into a different test source root of the same module - util methods are imported from the existing util class from another test source root (no new util class is created)

Checklist (remove irrelevant options):

• The change followed the style guidelines of the UTBot project
• Self-review of the code is passed
• The change contains enough commentaries, particularly in hard-to-understand areas
• New documentation is provided or existed one is altered
• No new warnings
• New tests have been added
• All tests pass locally with my changes