Fix: Apply unscaled padding to Viewport inside WWT_INSET. (#9219)

Since pixel dimensions in SetPadding() are scaled by GUI size, padding for inset viewports was excessive.

Instead, automatically apply padding for WWT_INSET at widget level. This applies to all widgets inside a WWT_INSET, which in all instances is a NWID_VIEWPORT.

Fix: Vehicle list windows did not update when this year's profit changed

Remove caching from vehicle group object. and recalculate it whenever
required instead.

Codechange: Apply coding style (#8640)

* Fix: Missing or needed spaces

* Codechange: Remove space

* Codechange: Remove space

* Codechange: More missing spaces

* Codechange: Missing spaces

* Codechange: Remove space

* Codechange: Remove space

Fix #8272: vehicle destination text colour when mousing over (#8543)

Co-authored-by: Jonathan G Rennison <j.g.rennison@gmail.com>

Feature: Option to group vehicle lists by shared orders

This applies to all kinds of vehicle lists, as well as the "vehicle groups" window.

Codechange: Make vehicle lists internally support grouping of vehicles

This is in preparation for the new UI feature that allows grouping by shared orders.

Codechange: Switch DropDownList to directly use std::vector, thus making AutoDeleteSmallVector obsolete.

DropDownListItem are strongly managed using std::unique_ptr to ensure leak-free handling. Appropriate use
of move-semantics make intent a lot clearer than parameter comments and allows the compiler to generate
copy-free code for most situations.