"Extract MAF blocks" usage: prevent submit without required inputs

The tool will currently allow job submission even when the target genome is not specified - a required input. This results in a job that runs but always ends in cryptic error. Would be better if the tool submission button was not accessible until all inputs are resolved.

Likely impacts all tools from this same group: galaxy/tools/maf/

The target genome(s) are not available when the MAF is from the history and one of the following is true:
1. The job creating the MAF input has not completed yet
or
2. The MAF input is malformed

If the tool could prompt the user about the difference, that would enhance usage

"Selected MAF input is processing and cannot be used with this tool until complete."
"Selected MAF input does not contain any recognized genomes. Please verify MAF format."

Start by inspecting the tools in galaxy/tools/maf/ and tracing the submission flow for the “Extract MAF blocks” group. Done means submission is blocked when the target genome is unavailable, with distinct messages for a processing history input and a malformed MAF lacking recognized genomes.

Written by the indexing model from the issue text.