VSE: Fix of several outline and handle related problems by bracket handles

There are numerous problems with the current handles and outlines:
- Current handles are making waveform editing imprecise: T90824
- They are not showing a direction(previously they had arrows).
- Having both strip(via outline) and handles selection drawn is the cause of confusion: T90843
- Strip overlay texts are stealing attention away from with the selected elements.
- Adjoined outlines are drawn op top of each other.

Solutions:
- Change handles to bracket shaped(introduced in: D10297), so the waveform is not covered by the handle.
- Selection is drawn as either handle or strip, so there is no confusion(and it is in consistency with ex. 3d view where a selected object and a selected vertex are drawn at the same time).
- Since the handles are smaller this way, the overlay and transform texts colors are muted a bit, so selection will stand out as the most highlighted elements.
- The outlines have been tweaked, so the outlines are moved away from each other and a dark line is separating them.

Before
{F10768098,size=full}

After
{F10768103,size=full}

A gif:
{F10768170,size=full}

Differential Revision: https://developer.blender.org/D12308