This addresses warnings from Clang-Tidy's `readability-else-after-return`
rule in the `source/blender/editors/interface` module.
No functional changes.
The old convention was easy to confuse with ScrArea.
Part of https://developer.blender.org/T74432.
This is mostly a batch rename with some manual fixing. Only single word
variable names are changed, no prefixed/suffixed names.
Brecht van Lommel and Campbell Barton both gave me a green light for
this convention change.
Also ran clan clang format on affected files.
This affects the timeline, dopesheet, graph editor, sequencer,
clip editor and nla editor.
Removed structs and enums: `V2D_ARG_DUMMY`, `eView2D_Units`,
`eView2D_Clamp`, `eView2D_Gridlines`, `View2DGrid`.
A main goal of this refactor is to get rid of the very generic
`View2DGrid` struct. The drawing code became very complex
because there were many different combinations of settings.
This refactor implements a different approach.
Instead of one very generic API, there are many slighly
different functions that do exactly, what we need in the
different editors. Only very little code is duplicated,
because the API functions compose some shared low level code.
This structure makes the code much easier to debug and change,
because every function has much fewer responsibilities.
Additionally, this refactor fixes some long standing bugs.
E.g. when `Show Seconds` is enabled, you zoom in and pan the view.
Or that the step size between displayed frame numbers was
always `>= 2`, no matter how close you zoom in.
Reviewers: brecht
Differential Revision: https://developer.blender.org/D4776
