HOCON: removed Value node, introduced Concatenation node
(cherry picked from commit f12b500)
HOCON: reformat code, organize imports
(cherry picked from commit 6d1ad85)
HOCON: hierarchy of PSI stub classes, String node introduced
(cherry picked from commit 5e6e3a6)
HOCON: forcing single space after include keyword when formatting
(cherry picked from commit abe6057)
HOCON: Java class reference detection on string literals
(cherry picked from commit c0b803d)
HOCON: project settings to disable class reference detection
(cherry picked from commit 6c7889b)
HOCON: class references are soft
(cherry picked from commit a6a5b89)