index consistency fixes

* use last committed document stamp for unsaved/uncommitted documents
* during psi commit, return psi mod stamp and not the document's one
* during multi-tree psi commit, indices should use the main tree's AST content and not the semi-updated parallel trees
* consider documents committed after changes in absence of PSI
(cherry picked from commit 5e3b801)
prefer document's stamp over file's one in view provider (IDEA-128919)
(cherry picked from commit 3deea11)