[Feature] Add initial button position support for FastPR

[frank-zsy]

One more thing to add is the initial position of the button. Is the initial position reflected in the configuration file or elsewhere? Add a return item in the configuration file that represents several common positions such as top, bottom, left, right, bottom right, top right, etc

Originally posted by @wangyantong2000 in #905 (comment)

[frank-zsy]

Position description is good but absolute position or percentage could be much more convenient than several fixed preset.