stylo: Avoid using InterpolateMatrix as a fallback for matched transform function pair.

In the current implementation, if there is any interpolation error in a matched
transform function pair, we fall-back to use InterpolateMatrix unconditionally.
However, the error could be caused by:

1. mismatched transform function pair
2. matched transform function pair within at least one undecomposable matrix.

Using InterpolateMatrix for case 1 makes sense, however, using InterpolateMatrix
for case 2 does not. According to the spec, we should just report error for
case 2, and let the caller do the fallback procedure. Using InterpolateMatrix
for case 2 will go through more unnecessary code path, and produce more memory
usage and calculation cost, which should be avoidable.

In this patch, we add an extra pass to check if a transform function pair have
matched operations in advance. With this information, we can easily tell whether
the interpolation error in a equal-length transform function pair is caused by
case 1 or case 2. So, we can avoid the unnecessary cost.

Gecko bug: Bug 1399049

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