Changes to the HalfCheck operation logic of the tree component

[guxin0123]

What problem does this feature solve?

Some trees need to limit the maximum number of leaf nodes that can be selected.

Then when the parent node of the tree is half selected,

the parent node needs to clear the selected state of itself and its child nodes when clicking the checkbox.

What does the proposed API look like?

<nz-tree  nzCheckable  [nzHalfCheckAll]="true | false" ></nz-tree>

nzHalfCheckAll : true -> click half checkBox to chagee all childern checked = true

nzHalfCheckAll : false -> click half checkBox to chagee all childern checked = false