[LL FIR] FileStructure: resolve FirFile to body phase as all other elements

This is the correct behavior as we have to resolve to body phase
to build CFG and run diagnostics collector correctly

^KT-65780 Fixed

analysis/low-level-api-fir/testData/getOrBuildFir/annotations/fileAnnotationScript.txt

@@ -6,7 +6,7 @@ FIR element rendered:
 @FILE:R|kotlin/Suppress|[Types](names = vararg(String()))
 
 FIR FILE:
-FILE: [ResolvedTo(IMPORTS)] fileAnnotationScript.kts
+FILE: [ResolvedTo(BODY_RESOLVE)] fileAnnotationScript.kts
     @FILE:R|kotlin/Suppress|[Types](names = vararg(String()))
     [ResolvedTo(BODY_RESOLVE)] annotations container
     context(<script>@kotlin.script.templates.standard.ScriptTemplateWithArgs)