Add Element Equivalence Interfaces

[kwokcb]

Issue

Addresses issues: #1988 and #1981 dealing with comparison of element values by adding in a new "functionally" equivalent interface, such that functional equivalence means that the 2 elements perform the same computation. This differs from the existing operator== interface which checks for syntactical equivalence.

The key points for functional equivalence include:

• The order of attributes specified on an Element does not matter.
• The order of children Elements does not matter as long as these are immediate children of a Document or a Compound NodeGraph.
• Equivalence can be performed based on runtime values as opposed to the string value used for text storage. For floating point numeric values equivalence can be performed within a given precision tolerance and/or numeric format.
• Non-functional attributes may be explicitly skipped, such as UI formatting. UI numeric meta-data follows the same equivalence criteria as for input/output values (e.g. uimax or uimin). Name and Category equivalence cannot be skipped.

Changes

• Adds a new isEquivalent method to Element.
• Adds a new isAttributeEquivalent method for Element and override for ValueElement to allow for value vs string comparisons on the latter.
• Adds equivalence options class: ElementEquivalanceOptions which can be passed in as an argument to isEquivalent
• Adds an optional results / feedback class: ElementEquivalenceResult which can be passed in as an argument to isEquivalent and isAttributeEquivalent.

The following equivalence options are available:

• Floating point format and precision for a float ValueElement. This is the same precision mechanism used for all value<->string conversions including values for code generation and file I/O.
• The ability to skip a user provided list of attributes. e.g. skipping { xpos, ypos }.
• Perform raw string compares for values (as operator==) currently does instead of value comparisons for a ValueElement.

Implementation Notes

• Note that value comparisons convert from string to a concrete runtime type which will remove any
  extraneous string formatting such as leading and trailing spaces, 0 and leading + sign.
• The the Value's string representation is used to perform the actual comparison allow for support of precision options.

Tests

A new unit test has been added with various numeric variations to test values, ordering, and precision.
The document pair used for testing looks like this:

<materialx version="1.39">
  <input name="input0" type="boolean" value="false">
  <input name="input1" type="color3" value="  1.0,   +2.0,  3.0   ">
  <input name="input2" type="color4" value="1.0,   2.00, 0.3000, -4">
  <input name="input3" type="filename" value="filename1">
  <input name="input4" type="float" uimin="  0.0100 " uimax="  01.0100 " value="  1.2e-10  ">
  <input name="input5" type="float" uimin="  0.0100 " uimax="  01.0100 " value="  00.1000  ">
  <input name="input6" type="integer" value="  12 ">
  <input name="input7" type="matrix33" value="01.0,         2.0,  0000.2310,    01.0,         2.0,  0000.2310, 01.0,         2.0,  0000.2310       ">
  <input name="input8" type="matrix44" value="01.0,         2.0,  0000.2310, 0.100, 01.0,         2.0,  0000.2310, 0.100, 01.0,         2.0,  0000.2310, 0.100, 01.0,         2.0,  0000.2310, 0.100">
  <input name="input9" type="string" value="mystring">
  <input name="input10" type="vector2" value="1.0,   0.012345608">
  <input name="input11" type="vector3" value="  1.0,   +2.0,  3.0   ">
  <input name="input12" type="vector4" value="1.0,   2.00, 0.3000, -4">
</materialx>

and

<materialx version="1.39">
  <input name="input0" type="boolean" value="false">
  <input name="input1" type="color3" value="1, 2, 3">
  <input name="input2" type="color4" value="1, 2, 0.3, -4">
  <input name="input3" type="filename" value="filename1">
  <input name="input4" type="float" value="1.2e-10" uimin="  0.01" uimax="  1.01">
  <input name="input5" type="float" value="0.1" uimin="  0.01" uimax="  1.01">
  <input name="input6" type="integer" value="12">
  <input name="input7" type="matrix33" value="1, 2, 0.231,  1, 2, 0.231,  1, 2, 0.231,  1, 2, 0.231">
  <input name="input8" type="matrix44" value="1, 2, 0.231, 0.1, 1, 2, 0.231, 0.1, 1, 2, 0.231, 0.1, 1, 2, 0.231, 0.1">
  <input name="input9" type="string" value="mystring">
  <input name="input10" type="vector2" value="1, 0.012345611">
  <input name="input11" type="vector3" value="1, 2, 3">
</materialx>