[RFC] Drop support for Visual Studio 2015?

[jameslamb]

Description

According to https://learn.microsoft.com/en-us/visualstudio/productinfo/vs-servicing#older-versions-of-visual-studio, Microsoft will fully drop support for Visual Studio 2015 in 9 months (October 2025).

Should LightGBM drop support for it after the v4.6.0 release (#6796)?

Benefits of this work

• would allow for updating to newer versions of dependencies ([c++] update to fmt 11.1.2, fast_double_parser 0.8.0 #6802 (comment))
• reduces maintenance burden

Approach

LightGBM uses Appveyor to test the oldest supported Visual Studio. So this change would mean updating this:

LightGBM/.appveyor.yml

Line 3 in 3aac25a

image: Visual Studio 2015

To Visual Studio 2017 (ref: https://www.appveyor.com/docs/build-environment/#build-worker-images

[StrikerRUS]

I don't mind.