Check for valid secondary tags of power plant and generator

[skyper]

Working on #21398 I came to the conclusion that we could have some validator warnings ​comparing the output of the plant and the enclosed generators and for wrong combinations of method and source for generator and plant on their own and comparing between plant and its enclosed generators.

• warn about wrong combination of generator:source and generator:method
• warn about wrong combination of plant:source and plant:method
• warn if plant:source does not equal all enclosed generator:source
• warn if plant:method does not equal all enclosed generator:method

• warn if sum of plant:output does not equal the sum of all enclosed generator:output
  • could be split into several depending on the plant sum being greater or small than the generator sum.

Or do we get too many false positives as backup/emergency generators do count.