Codechange: Remove direct access to _colour_gradient.

Access is now through GetColourGradient, which ensures parameters are in range.

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: Add __FILE__/__LINE__ of WindowDesc to WindowDesc.

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

Add: data parameter in Window::Close method.

This allows passing data when closing a window, e.g. to indicate how it was closed.

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: Base CargoArray off std::array.

This avoids needing to define array accessors and allows use of
default value initialization.

Fix #10819, Fix #10811: GetVehicleFromDepotWndPt used widget- instead of window-relative positions. (#10820)

Pass window-relative positions instead, and adjust for relative positions where needed within the function itself. This simplifies calling code.

Codechange: Use GetScrolled(Row/Item)FromWidget in more places.

In many instances the clicked row position is 'manually' calculated
instead of using the GetScrolledRowFromWidget helper function, with
variations on checks. Replace with the two helpers where possible.

Codechange: Scrollbar methods now accept size_t.

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

Fix #10114: Wonky depot layout. (#10191)

Depot lists internal layout was not handled well. This is improved by
throwing more Rects at it:
- Vehicle images are now be vertically centred in the rect.
- Image clipping is relaxed to cover the rect, improving larger sprites.
- Outline highlight is now aware of bevel thickness.

Change: Use power-of-2 scaling for some dimensions in GUI.

These are related to drawing sprites that are normally drawn on the
landscape, and should therefore still follow power-of-2 scaling to fit
correctly.

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.

Cleanup: nested_array should not be accessed directly.

Replace accesses with GetWidget() as documented.

Codechange: Spell 'Viewport' consistently

Some places in the codebase misspell 'Viewport' as 'ViewPort' or 'view_port'.
This patch makes everything consistent.