Simply clicking once on a block should not place it

It is very confusing when people just click on a block, either in a function or list comprehension, or from the toolbox, and a copy of that block gets placed in the workspace. We should wait for some minimum drag distance before treating this as a drag.

通过在函数、列表推导式和工具箱中点击块（不进行拖动）来复现该行为。定位区分点击和拖动的块交互处理逻辑，然后验证点击不会放置副本，而拖动超过所选的最小距离仍会放置副本。

由索引模型根据 Issue 内容生成。