modernize lineinfos; it seems that array access hinders strict def analysis like field access (#22420)

modernize lineinfos; array access hinders strict def analysis like field access

A bug ?

```nim
proc computeNotesVerbosity(): array[0..3, TNoteKinds] =
  result[3] = {low(TNoteKind)..high(TNoteKind)} - {warnObservableStores, warnResultUsed, warnAnyEnumConv, warnBareExcept}
  result[2] = result[3] - {hintStackTrace, hintExtendedContext, hintDeclaredLoc, hintProcessingStmt}
  result[1] = result[2] - {warnProveField, warnProveIndex,
    warnGcUnsafe, hintPath, hintDependency, hintCodeBegin, hintCodeEnd,
    hintSource, hintGlobalVar, hintGCStats, hintMsgOrigin, hintPerformance}
  result[0] = result[1] - {hintSuccessX, hintSuccess, hintConf,
    hintProcessing, hintPattern, hintExecuting, hintLinking, hintCC}
```

Author: ringabout

compiler/lineinfos.nim

@@ -7,8 +7,8 @@
 #    distribution, for details about the copyright.
 #
 
-## This module contains the ``TMsgKind`` enum as well as the
-## ``TLineInfo`` object.
+## This module contains the `TMsgKind` enum as well as the
+## `TLineInfo` object.
 
 import ropes, tables, pathutils, hashes
 
@@ -248,6 +248,7 @@ type
   TNoteKinds* = set[TNoteKind]
 
 proc computeNotesVerbosity(): array[0..3, TNoteKinds] =
+  result = default(array[0..3, TNoteKinds])
   result[3] = {low(TNoteKind)..high(TNoteKind)} - {warnObservableStores, warnResultUsed, warnAnyEnumConv, warnBareExcept}
   result[2] = result[3] - {hintStackTrace, hintExtendedContext, hintDeclaredLoc, hintProcessingStmt}
   result[1] = result[2] - {warnProveField, warnProveIndex,
@@ -341,9 +342,8 @@ type
 
 
 proc initMsgConfig*(): MsgConfig =
-  result.msgContext = @[]
-  result.lastError = unknownLineInfo
-  result.filenameToIndexTbl = initTable[string, FileIndex]()
-  result.fileInfos = @[]
-  result.errorOutputs = {eStdOut, eStdErr}
+  result = MsgConfig(msgContext: @[], lastError: unknownLineInfo,
+                     filenameToIndexTbl: initTable[string, FileIndex](),
+                     fileInfos: @[], errorOutputs: {eStdOut, eStdErr}
+  )
   result.filenameToIndexTbl["???"] = FileIndex(-1)