Cleanup: Use ELEM Macro

Fix T77289: Crash when typing negative numbers

This was caused by an oversight in rB45dbc38a8b15. When the next operation
character is found the offset is shifted in the original string. The remaining
length has to be recalculated with that offset before shifting the remaining
characters to make room for the ")".

Revert "UI: Fix T77173: Report Background Colors for 2.83 Release"

This reverts commit 7fc0053c27e5e9ba3cc946898c7c11a8545f2777.

Merge branch 'blender-v2.83-release'

UI: Fix T77173: Report Background Colors for 2.83 Release

This is a temporary solution for T77173 for the 2.83 release. D7203
provides a more long term solution for future releases.

This adds theme colors for the three report backgrounds, setting them
to the color used in 2.82. A separate commit in the addons repository
will follow for changes to the bundled themes.

Differential Revision: https://developer.blender.org/D7908

Cleanup: Use const context for some UI templates

- uiTemplateID: Straightforward, just const for the template
and the functions it calls
- uiTemplateCacheFile: Create a function in rna_ui.c because
the generated RNA callback doesn't have const context.

Differential Revision: https://developer.blender.org/D7895

Cleanup: Remove Obsolete Current Frame Indicator Drawing Code

This code was made obsolete by the changes to the animation editor
scrubbing areas in D4654.

Differential Revision: https://developer.blender.org/D7898

UI: Rename "View Camera Center" Op to "Frame Camera Bounds"

The current name isn't very specific about what the operator does.
The operation is more about lining up the edges with the viewport
edges than centering the view.

Differential Revision: https://developer.blender.org/D7866

Fix T77139: UI: Add "View Camera Center" to View Menu

The "View Camera Center" operator was not accessible by the new menu search.

Differential Revision: https://developer.blender.org/D7865

Fix T74552: Distribute negatives in number input

This applies a relatively simple solution for fixing some unintuitive
cases in unit handling.

Currently entering -1m50cm evaluates to -0.5m, and similarly 1'6"
evaulates to just half a foot. So effectively there's an implied + just
between the numbers, which is quite confusing.

This works by adding parentheses so the negative distributes to the
block of values before the next operator.

For example:
| Before | After |
| `-1m50cm + 1m -2m50cm` | `-(1m50cm) + 1m -(2m50cm)` |
| `-4m + 0.5 / -1.1` | `-(4m) + 0.5 / -(1.1)` |
| `-1'6"` | `-(1'6")` |
| `-1e-2cm` | `-(1e-2cm) ` |

Reviewed By: campbellbarton

Differential Revision: https://developer.blender.org/D7813