Add a windowRawText property to braille.BrailleBuffer (#7354)
* Added the following to the braille.BrailleBuffer class:
* Properties rawText, rawToBraillePos and brailleToRawPos; based on the properties for braille.Region, but for the entire buffer
+ These are updated in braille.brailleBuffer.update
* bufferPositionsToRawText method: accepts two buffer positions and returns the portion of raw text associated with the given positions
* windowRawText property: contains the raw text for the current window
* rawToBraillePos and brailleToRawPos are now dynamic
* Cache brailleToRawPos and rawTobraillePos
Author
Leonard de Ruijter
