feat: alias \dot and \cdot to \centerdot (#639)

Discussed at [#lean4 > \cdot != \centerdot @
💬](https://leanprover.zulipchat.com/#narrow/channel/270676-lean4/topic/.5Ccdot.20!.3D.20.5Ccenterdot/near/528312220).

Author: mhuisi

lean4-unicode-input/src/abbreviations.json

@@ -492,7 +492,7 @@
     "doteq": "≐",
     "dotplus": "∔",
     "dotsquare": "⊡",
-    "dot": "⬝",
+    "dot": "·",
     "dong": "₫",
     "downarrow": "↓",
     "downdownarrows": "⇊",
@@ -991,7 +991,7 @@
     "colon": "₡",
     "copyright": "©",
     "cdots": "⋯",
-    "cdot": "⬝",
+    "cdot": "·",
     "cib": "●",
     "ciw": "○",
     "ci..": "◌",