In K1, code fragment analysis was completely invalidated on any PSI
change. Because imports are not a part of the PSI tree of
'KtCodeFragment's, a colon tremble happened on 'addImportsFromString()'.
In K2, changes inside code fragments are always considered in-body
modifications. So, even with the colon trembling, the 'FirFile',
together with its 'FirImport's was not recreated.
^KT-65600 Fixed
Yan Zhulanow
1c1da6bced