Improve hover service

[kittaakos]

Bug Description:

1. When there is insufficient space for the hover, Theia calculates a fallback hover position. It does not always work.

hover.mp4

2. I can make the hover visible, although the cursor is neither over the host nor the target.

theia_hover_01.mp4

3. Hovering over the popup does not work reliably.

theia_hover_02.mp4

4. Top calculation logic should count with the status bar height. In other words, do not hover over the status bar.

theia_hover_03.mp4

5. For the markdown links, styles should be improved:

theia/packages/core/src/browser/style/hover-service.css

Lines 43 to 49 in ff944de

	.theia-hover a {
	color: var(--theia-textLink-foreground);
	}
	.theia-hover a:hover {
	color: var(--theia-textLink-active-foreground);
	}

.theia-hover a {
    color: var(--theia-textLink-foreground);
    word-wrap: break-word; /* customized */
    cursor: pointer; /* customized */
}

.theia-hover a:hover {
    color: var(--theia-textLink-active-foreground);
    text-decoration: underline; /* customized */
}

Steps to Reproduce:

1. See the screencasts.

Additional Information

• Operating System: macOS
• Theia Version: Theia Blueprint Version 1.35.0 (1.35.0.98)