Container class containing UTF-32 platform-endian encoding.

@see Class Comments in <EsUnicodeEncoding> for usage examples.

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asUnicodeString:

<pre><code>   Answer a new unicode string instance from the receiver.    If @repair is true, then invalid utf32 will be replaced with the unicode replacement character U+FFFD.   
   Examples:     'Grinning Face (U+1F600)'.     self assert: [(Utf32LE with: 16r1F600) asUnicodeString first name = 'GRINNING FACE'].          'Invalid UTF32-encoding'.     self assert: [[(Utf32LE with: 16rD800) asUnicodeString. false] on: Exception do: [:ex | ex exitWith: true]].          'Repaired invalid UTF8-encoding'.     self assert: [((Utf32LE with: 16rD800) asUnicodeString: true) = UnicodeScalar replacementCharacter asUnicodeString].

   Arguments:     repair - <Boolean>    Answers:     <UnicodeString> </code></pre> </details>

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isValid

   Answer true if the content of the container represents valid UTF-32 data
   encoded in the endian type defined by the container.
   
   Examples:
    'Grinning Face (U+1F600) in platform endian'.
    self assert: [
      System bigEndian
        ifTrue: [(Utf32 with: 16r1F600) isValid]
        ifFalse: [(Utf32 with: 16r1F600) isValid]].
    
    'Invalid because of isolated surrogate - 16rD800'.
    self assert: [(Utf32LE with: 16r1F600 with: 16rD800) isValid not]
   
   Answers:
    <Boolean> true if valid, false if invalid

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