[FIR] Don't enhance Int and String Java final static fields

It's effectively a breaking change (^KT-62558)

K2 assigns flexible type to all static fields (from Java) and, for example,
`String? becomes String unlike K1. It affects IR signature generating.
That's why signature dump is disabled for some tests.

^KT-57811 Fixed
^KT-61786 Fixed

compiler/fir/analysis-tests/testData/resolveWithStdlib/j+k/StaticFromBaseClass.fir.txt

@@ -1,5 +1,5 @@
 FILE: main.kt
     public final fun test(): R|kotlin/Unit| {
-        lval project: R|kotlin/String| = Q|PlatformDataKeys|.R|/CommonDataKeys.PROJECT*s|
+        lval project: R|kotlin/String!| = Q|PlatformDataKeys|.R|/CommonDataKeys.PROJECT*s|
         lval member: R|kotlin/String!| = R|/PlatformDataKeys.PlatformDataKeys|().R|/CommonDataKeys.MEMBER|
     }