Determine upper or lowercase for SynExpr.DotIndexedGet

[nojaf]

Fixes #798

[Smaug123]

It's not clear to me what this pattern is actually matching (due to me not having much experience with Fantomas). Is the point that we were previously unable to tell that the a in a.A.[0] was a lowercase expression?

[nojaf]

The pattern match tries to determine if the SynExpr is upper- or lowercase.

In this case, the problem was that SynExpr.DotIndexedGet was passed to the function and was not yet supported.
Looking at the structure of the DotIndexedGet, its first value in the tuple is a SynExpr so we can the function recursively in this case.

DotIndexedGet
                       (LongIdent
                          (false,
                           LongIdentWithDots
                             ([a; A],[tmp.fsx (1,16--1,17) IsSynthetic=false]),
                           None,tmp.fsx (1,15--1,18) IsSynthetic=false),
                        [One
                           (Const
                              (Int32 0,tmp.fsx (1,20--1,21) IsSynthetic=false),
                            false,tmp.fsx (1,20--1,21) IsSynthetic=false)],
                        tmp.fsx (1,18--1,19) IsSynthetic=false,
                        tmp.fsx (1,15--1,22) IsSynthetic=false)

=> determine value of DotIndexedGet by checking SynExpr.LongIdent.