This reverts commit 7435c68b.

 * PythonPathCache managed to return nulls for collected soft references

IDEA-168864 Run Configuration - dirty state is not changed after adding any action to Before launch section

1. test might check precisely this failure
2. even if not, the test will fail anyway and the mistake will be obvious quite soon

don't commit in next/prev parameter action update (EA-97963 - assert: PsiDocumentManagerBase.commitAllDocuments)

* fix StringIndexOutOfBoundsException from (CPP-8843);
* remember compiled Pattern instead of Matcher;
* problem was introduced in c1180cfb

which file returns invalid context? (EA-85729 - PIEAE: PsiInvalidElementAccessException.createByNode)

support SharedIndicesData.ourFileSharedIndicesEnabled, forward index becomes nullable for SharedMapBasedForwardIndex

Follows-up: IDEA-CR-18741 testFramework: (testing) Add UsefulTestCase.assertThrows()