sw: remove silly BigInt based SqRt

Change-Id: I0a23682998fcf23f917289a0137d137b240a9d92
fdo#70232: sw: brown paper-bag fix for header sharing mangling footers

Stupid copy/paste error in SwDoc::CopyMasterFooter() checks
IsHeaderShared().

(regression from e1a9a348a519a69f898c9c1e6d87a5837b8267f9)

Change-Id: I0c0bc16a8c581cd05ed206a0de79c7983204165b
fdo#69065: sw: fix mirrored page style with first-page

If a mirrored page style is used with first-page on both a right page
and a left page the current design cannot work because the margins in
the SwPageDesc::aFirst cannot be right for both cases.

So split that up so we get a first-master and first-left format and
copy the headers/footers and margins as appropriate... which is really
adding epicycles to a flawed design; probably this would be better with
just a single SwFrmFmt that has different items for master/left/first
headers.

Change-Id: I0889a4ab5959b5a71172203bb64d185960a07d73
fdo#71429: sw: fix crashes when changing header first sharing

Copy some nutso code in SwUndoPageDesc::ExchangeContentNodes() to
work on the un-shared First header/footer too, which apparently avoids
the crash.  It's not like Undo of header/footer isn't already a
house of cards anyway.

Change-Id: Ie6593c4784ce9d368a5098ffb3aa4dec536d250e