ImageMatching: Only require featuresFolders when it is relevant to the matching method

[servantftransperfect]

Description

The Exhaustive and Sequential image matching methods do not read features or descriptors. They build image pairs only from the list of views. Even so, the featuresFolders parameter was always shown in the ImageMatching nodes, and the aliceVision_imageMatching executable required it.

This PR disables the parameter in Meshroom when it is not used, and makes it optional on the command line.

Changes

• Meshroom nodes (ImageMatching, ImageMatchingMultiSfM): featuresFolders is now disabled when method is Exhaustive or Sequential.
• main_imageMatching.cpp:
  • --featuresFolders moved from required to optional parameters. Meshroom does not pass disabled attributes on the command line, so leaving the option required would make these runs fail.
  • When the selected method needs descriptors (any method other than Exhaustive and Sequential), the program checks that features folders were provided. If none were, it logs an error and exits with a failure code.

Notes

• Behaviour is unchanged for the vocabulary tree, Frustum and Mirror methods. They still need featuresFolders.
• ImageMatchingMultiSfM has no plain Sequential method. In that node, only Exhaustive disables the parameter.