fix(show-hide): display set to "initial" value if parent has no display set

[vmasek]

When SSR creates media screen styles it sets the default display to parent.display, but if the parent has its display property unset, it results in an empty display which breaks the correct functionality as the next closest match is made.

Fixed by setting display to initial as default instead of an empty value.

fixes #1163

[vmasek]

As I see the tests fail, I'm not sure if this actually breaks something or how to altern the tests to match this behaviour. Please leave feedback on what do you think and I'll try to fix it.

[gurkan0791]

It's my understanding that I should add "fxLayout" to all "mat-header-cell" and "mat-cell" tags?Otherwise it will be corrupted due to "display: initial".
For Example, Stackblitz

[CaerusKaru]

@gurkan0791 I’m a little confused by your comment; can you open an issue with your StackBlitz along with what you think the expected behavior should be?

[CaerusKaru]

Tracking in #1250

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