SMM — Improve Label format support

This is a small improvement upon the initial implementation of label format support.

Discussion:
The labelFormat attribute was added to the Measure class in issue #14101. Since then it has been noticed that there are actually 2 main use cases for labels. The first one is to provide a label that describes the measure and the other one is to provide a label describing the measurement. This issue addresses this shortcoming.

Secondly, we are also here expanding the use of the Operation class by changing the specification of the label format in order to have queries simply defined in terms of Operations instead of declaring the query and its language within the label format.

Summary of change:
· Add new attribute and change name of existing one.
o Rename attribute labelFormat:String in Measure class to measureLabelFormat:String
o Add attribute measurementLabelFormat:String in Measure class.
· Add new operations and change name of existing ones.
o Rename operation getLabel():String in Measurement class to getMeasureLabel():String
o Add operation getMeasurementLabel():String in Measurement class.
· Change specification of labelFormat to support use of Operation
o Change wording of standard syntax to the following:
§ The standard syntax, which is always valid, starts by specifying a context object, followed by a literal colon ":", then an operation whose name must be the name of a valid instance in the Operation class.

• Add new attribute and change name of existing one.
o Rename attribute labelFormat:String in Measure class to measureLabelFormat:String
o Add attribute measurementLabelFormat:String in Measure class.
• Add new operations and change name of existing ones.
o Rename operation getLabel():String in Measurement class to getMeasureLabel():String
o Add operation getMeasurementLabel():String in Measurement class.
• Change specification of labelFormat to support use of Operation
o Change wording of standard syntax to the following:
? The standard syntax, which is always valid, starts by specifying a context object, followed by a literal colon “:”, then an operation whose name must be the name of a valid instance in the Operation class.