Refactor XMLTester

[dr-jts]

Improves XMLTester by modularizing it using an additional Test class and a few lambda functions. This allows factoring out common code to achieve DRY.

• improves maintainability
• easier to add new operations
• reduces risk of ops missing expected behaviour (e.g. swapping A and B args, test reporting)
• reduces code size (> 800 lines removed)
• adds test file line number reporting

This has also uncovered some issues with result testing (in particular, using topological rather than exact equals). Fixing this requires fixing a few tests, so will be done in a subsequent PR.