Use GetFullPath when determining the full path in command line options

[cartermp]

Fixes #4016, #5521, #4446

This is @chadunit's idea here: #4016 (comment)

Quick writeup:

• When QuickInfo navigation is built out, it uses ranges coming from the actual F# symbol(s) it has access to. The ranges for these symbols include path information that has been normalized.
• When f12 is invoked, it calls into a route that creates a range type based on the file name that the editor host supplies.
• The VS editor host did not normalize file paths prior to this change, so the 2nd point means that the range types created won't match actual ranges that live on a symbol
• This discrepancy causes a failure in an equality check in name resolution
• This equality failure results in an inability to navigate to the symbol under the caret

[TIHan]

After this, we should cherry pick it into release/dev16.3 - looks good. When we tested, it seems to fixed the issue with navigation.