Add: [Script] GSIndustry.GetConstructionDate() method

[andythenorth]

Motivation / Problem

• For features or gameplay changes:
  • What was the motivation to develop this feature?
    • Provide GS with access to industry construction date
  • Does this address any problem with the gameplay or interface?
    • GS did not have access to industry construction date
  • Which group of players do you think would enjoy this feature?
    • Players who wish to use GS that depends on industry construction date

Description

Describe here shortly

• For features or gameplay changes:
  • What does this feature do?
    • Provides GS with access to industry construction date
  • How does it improve/solve the situation described under 'motivation'.
    • GS has access to industry construction date

Limitations

Describe here

• Is the problem solved in all scenarios?
  • Yes
• Is this feature complete? Are there things that could be added in the future?
  • Yes. No.
• Are there things that are intentionally left out?
  • No
• Do you know of a bug or corner case that does not work?
  • No

Checklist for review

Some things are not automated, and forgotten often. This list is a reminder for the reviewers.

• The bug fix is important enough to be backported? (label: 'backport requested')
  • No
• This PR touches english.txt or translations? Check the guidelines
  • No
• This PR affects the save game format? (label 'savegame upgrade')
  • No
• This PR affects the GS/AI API? (label 'needs review: Script API')
  • ai_changelog.hpp, gs_changelog.hpp need updating.
    • Yes, needs updating
  • The compatibility wrappers (compat_*.nut) need updating.
    • Don't know
• This PR affects the NewGRF API? (label 'needs review: NewGRF')
  • newgrf_debug_data.h may need updating.
    • No
  • PR must be added to API tracker
    • No

[glx22]

As you mentioned in the checklist, you need to update changelog :)

[rubidium42]

The compat scripts only need to be updated when some API gets changed. This is just a simple addition.