Let blink animation support style inheritance

[Martin1994]

With this change, blinking cursor will use the same font and background
color that set before, so that changing the style of cursor automatically applies to the animation.

Example:

In demo, change the background color to some light color and foreground color to some dark color, then enable blink:

#terminal-container .terminal {
    background-color: #ccc;
    color: #333;
    padding: 2px;
}

#terminal-container .xterm-viewport {
    background-color: #ccc;
}

#terminal-container .terminal:not(.xterm-cursor-style-underline):not(.xterm-cursor-style-bar) .terminal-cursor {
    background-color: #333;
    color: #ccc;
}

#terminal-container .terminal:not(.focus) .terminal-cursor {
    outline: 1px solid #333;
    outline-offset: -1px;
    background-color: transparent;
}

cursorBlink off:

Expected (and actual with this PR):

Actual (without this PR):

[Tyriar]

Can you provide some repro steps illustrating the problem? Is this if you're using a custom foreground color?

[Martin1994]

Hi @Tyriar I've updated the repro steps.

[Tyriar]

Perfect, thanks for the contribution 😃