@NotNull/Nullable

(cherry picked from commit 856f74b06fc43003efbaf1fdea1080b161c9b752)
[vcs] IDEA-122530 Fix deadlock in VCS instantiation

* VcsEP: still allowing non-synchronized component instantiation,
  synchronize access to myVCS to ensure myVcs is always the same.
* getByName: don't sync access to getVcs since it is synchronized
  internally.

(cherry picked from commit 0ed49120d2287483a15f73e8e1c2d8d861bbcf08)