Codefix: DrawEngineList does not accept EngineID.

Replace min/max parameters of DrawEngineList with scrollbar reference, and use iterators instead of indices.

Codechange: Make all NWidgetPart arrays constexpr.

This ensures that the arrays are not created at runtime and prevents using non-constexpr values.

Codechange: Replace mishmash of types for widget index with WidgetID.

Indices were stored as int, but often passed around as uint/uint8_t and casts.

Now they should all use WidgetID.

Codechange: Remove FONT_HEIGHT_... macros. (#11481)

These make it look like we're dealing with a constant, but actually each is a call to `GetCharacterHeight(...)`.

Codechange: Simplify autoreplace rail/road types by using separate widget. (#11457)

This avoids needing to determine which type of list to deal with by additionally checking the window number for VEH_TRAIN/VEH_ROAD.

Codechange: Add __FILE__/__LINE__ of WindowDesc to WindowDesc.

This is to allow unit-tests to produce more useful output.

Codechange: Avoid emplace_back(new()) into a unique_ptr. (#11384)

This could theoretically leave an unmanaged pointer in certain circumstances, and directly using
make_unique shows intent.

Fix 94167dfd: Don't shade the currently selected engine in autoreplace window. (#11354)

This breaks #7729 which specifically allows autoreplace of same engine types, and also did not work properly if the engine had been built during the current game session.

Codechange: Use begin/end of nwidget parts of begin/length.

This simplifies processing nwidget parts as, unlike the remaining length, the pointer to the end of the list never changes. This is the same principle as we use(d) for tracking end instead of length for C-style strings.

And this removes 160~ instances of the lengthof() macro.

Codechange: automatic adding of _t to (u)int types, and WChar to char32_t

for i in `find src -type f|grep -v 3rdparty/fmt|grep -v 3rdparty/catch2|grep -v 3rdparty/opengl|grep -v stdafx.h`; do sed 's/uint16& /uint16 \&/g;s/int8\([ >*),;[]\)/int8_t\1/g;s/int16\([ >*),;[]\)/int16_t\1/g;s/int32\([ >*),;[]\)/int32_t\1/g;s/int64\([ >*),;[]\)/int64_t\1/g;s/ uint32(/ uint32_t(/g;s/_uint8_t/_uint8/;s/Uint8_t/Uint8/;s/ft_int64_t/ft_int64/g;s/uint64$/uint64_t/;s/WChar/char32_t/g;s/char32_t char32_t/char32_t WChar/' -i $i; done

Codechange: Pass reference instead of pointer to GUI*Lists. (#10822)

Pointer-avoidance.

Codechange: Add and use GetScrolledItemFromWidget to get a list item.

This function returns an iterator, either to the selected item or the
container's end.

This makes handling the result more robust as indices are not used.

Codechange: Scrollbar methods now accept size_t.

This clears up a lot of casts from size_t to int.

Fix #10032: Capacities of articulated vehicles in build window

See also: #9954

Feature: Vehicle add-ons can now group engines in purchase list.

Grouped engines are collapsed by default but can be expanded. This allows
similar engines to be grouped together to avoid cluttering the list.

Suggested uses for this are e.g.:
* Liveries; same stats but different paint job.
* Re-gearing; engine design is mostly the same but different stats.

... but avoiding complex hidden cargo subtype refit systems.

Grouped engines are otherwise separate, so can be independently
autoreplaced, even between variants.

Change: Use Rect helpers for widget drawing.

This replaces repetitive and sometimes unwieldy use of constants.

Codechange: Template DoCommandP to automagically reflect the parameters of the command proc.

When finished, this will allow each command handler to take individually
different parameters, obliviating the need for bit-packing.

Codechange: use setting name instead of index for CmdChange(Company)Setting (#9306)

This is mostly done as there are now constraints on settings.ini you might not
expected. For example, conditional settings always have to come last, as otherwise
they would influence the index.

Fix: Count engine details text in lines rather than pixels. (#9107)

This allows the details panel to scale correctly for different zoom levels.

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.

(svn r20453) -Codechange: Remove direct accesses to Window::hscroll, vscroll and vscroll2.
Note: All windows get individual members with the same names, which are initialised via Window::GetScrollbar(). This caching is not required at all, but simplifies conversion.