fix: support CornerPlacement for port

[Crystal-RainSlide]

Unlike badges (whose placement is handled by getTextStyleByPlacement(), which supports CornerPlacement), ports don't support CornerPlacement like top-left. This PR fixes this by adding keys in CornerPlacement to PORT_MAP.

Also, document related to ports is missing content. It don't mention its key and placement prop:
https://g6.antv.antgroup.com/api/elements/nodes/base-node#连接桩样式-ports
Readers can only guess the placement prop from the document about badges beside it.

This fix don't calculate the position with node border. Thus it only works for the corner of rect-shaped nodes. Better note about this when adding document about ports.

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The 2nd commits improves packages/g6/src/utils/element.ts with:

• rename param for PORT_MAP from ports to the more accurate portMap.
• getConnectionPoint() is calling getNodeConnectionPoint() with param node: Node | Combo,
  but getNodeConnectionPoint() only has param node: Node. Changed it to nodeLike: Node | Combo.
• optimized getTextStyleByPlacement(), saved one ternary operator with the top and bottom constants.
• for setAttributes(), add type Partial<BaseShapeStyleProps> to param style to match with element: BaseShape<any>.
• improve comments for some params.

For packages/g6/src/utils/edge.ts, the 3rd commit replaces array[array.length - 1] with array.at(-1).
array.at()'s typing is static, it always return a type that includes undefined, regardless of situation.
Since controlPoints are [Point, Point], controlPoints.at(-1) can only be Point.

For packages/g6/src/runtime/layout.ts, the 3rd commit replace two slow, irrational for of loop + array.indexOf() with faster, reasonable for loop.

[zhongyunWan]

It is truly excellent news. We have observed that you possess a remarkable level of enthusiasm for contributing, and we eagerly anticipate collaborating with you on additional G6-related projects in the subsequent period.😄