XTCE12 — FixedValueEntry@sizeInBits should be required

FixedValueEntry@sizeInBits should be required

Propose to accept that FixedValueEntry ought to have @sizeInBits

It does make sense that FixedValueEntry in the CommandContainer should have a mandatory @sizeInBits. It also can have an optional @name to identify the fixed field. Add documentation for the usage of the new and existing attributes of the FixedValueEntryType.

Replace the existing definition of the complexType FixedValueEntryType with this updated definition.

<complexType name="FixedValueEntryType">
<complexContent>
<extension base="xtce:SequenceEntryType">
<attribute name="name" type="string" use="optional">
<annotation>
<documentation xml:lang="en">An optional name for the fixed/constant field in the sequence.</documentation>
</annotation>
</attribute>
<attribute name="binaryValue" type="hexBinary" use="required">
<annotation>
<documentation xml:lang="en">The fixed/constant value that should be encoded into the sequence. This value provided should have sufficient bit length to accomodate the size in bits. If the value is larger, the most significant unnecessary bits are dropped. The value provided should be in network byte order for encoding.</documentation>
</annotation>
</attribute>
<attribute name="sizeInBits" type="xtce:PositiveLongType" use="required">
<annotation>
<documentation xml:lang="en">The number of bits that this fixed/constant value should occupy in the sequence.</documentation>
</annotation>
</attribute>
</extension>
</complexContent>
</complexType>