[Enhancement] Improved tooltips and "invalid upstream" handling for Local Branches

[goran-w]

When un-/hovering a branch with a "Invalid upstream!" warning-icon under LOCAL BRANCHES, the mentioned icon jumps sideways in a visually unpleasing way (since the visibility eye-icon-button dis-/appears on un-/hover and nudges the other icon leftwards).

Additionally, if we move the mouse pointer towards that icon to check its tooltip, we end up getting the general branch-tooltip instead since the warning-icon (which ought to have its own tooltip, btw) jumps out of the way just when we expected to reach it.

Finally, the general branch-tooltip shows the upstream TRACKING branch, but without any indication that it's now "invalid"!

I'd suggest the following small but useful improvements:

• Align the warning-icon immediately to the right of the branch name - that way it won't jump around when hovering.
• Remove the icon-specific tooltip from the warning-icon, and instead add the same icon and message-text "Invalid upstream!" inside the general branch-tooltip.
• Add a icon-specific tooltip for the visibility eye-icon-button, to clarify what it does. (Currently the general branch-tooltip appears instead, which looks quite confusing as a tooltip specifically for the highlighted button!)

[goran-w]

@love-linger Thank you for fixing the tooltips! Could we also re-align the warning-icon so it no longer jumps sideways when hovering? It could either be attach immediately to the right of the actual branch-title text, or moved to the left side of the branch-title (i.e next to the ordinary branch icon).