fix(style): apply correct flex with ngStyle and layout change

[Teamop]

Fix #700
For this issue, I found that the flex is initialized to '1 1 0%', when the layout changes, the layout event triggers before ngStyle, so invokes _updateStyle to apply this initialization to the ngStyleBase. Then for the following ngStyle.lt-md event, just merge this base style.

So the change is: when the input changes in the StyleDirective, check the base style, if it's not same with the current style, replace it with the current style and for others which have been merged with ngStyleBase, delete the corresponding style and merge again.

In the following test cases, the first case is just like the scenario in the #700

[Teamop]

Failure in SSR: 1) style directive should allow more than one responsive breakpoint on one element

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