Add support of String Interpolation

[nojaf]

Issue created from fantomas-online

Code

let x = 1
let pi = 3.1414
let text = "cats"

let s = $"I say {x} is one and %0.2f{pi} is pi and %10s{text} are dogs"

Error

Fantomas.FormatConfig+FormatException: Parsing failed with errors: [|tmp.fsx (5,9)-(5,11) parse error This token is reserved for future use;
  tmp.fsx (5,9)-(5,11) parse error Unexpected whitespace in binding;
  tmp.fsx (5,71)-(5,72) parse error End of file in string begun at or before here|]
And options: { SourceFiles = [|"tmp.fsx"|]
  ConditionalCompilationDefines = []
  ErrorSeverityOptions = { WarnLevel = 3
                           GlobalWarnAsError = false
                           WarnOff = []
                           WarnOn = []
                           WarnAsError = []
                           WarnAsWarn = [] }
  IsInteractive = false
  LightSyntax = None
  CompilingFsLib = false
  IsExe = false }
   at Fantomas.CodeFormatterImpl.parse@61-2.Invoke(FSharpParseFileResults _arg2) in /home/runner/work/fantomas-tools/fantomas-tools/.deps/fantomas/src/Fantomas/CodeFormatterImpl.fs:line 66
   at Microsoft.FSharp.Control.AsyncPrimitives.CallThenInvokeNoHijackCheck[a,b](AsyncActivation`1 ctxt, FSharpFunc`2 userCode, b result1) in F:\workspace\_work\1\s\src\fsharp\FSharp.Core\async.fs:line 416
   at <StartupCode$FSharp-Compiler-Service>.$Service.ParseFile@436-3.Invoke(AsyncActivation`1 ctxt) in /Users/chethusk/oss/FCS/src/fsharp/service/service.fs:line 436
   at Microsoft.FSharp.Control.Trampoline.Execute(FSharpFunc`2 firstAction) in F:\workspace\_work\1\s\src\fsharp\FSharp.Core\async.fs:line 109

Problem description

See https://github.com/fsharp/fslang-design/blob/master/RFCs/FS-1001-StringInterpolation.md.
I may have been a bit too eager when merging in FCS37.

Extra information

• The formatted result breaks by code.
• The formatted result gives compiler warnings.
• I or my company would be willing to help fix this.

Options

Fantomas Master at 08/13/2020 09:57:58 - ee6dd12

Name	Value
IndentSize	4
MaxLineLength	120
SemicolonAtEndOfLine	false
SpaceBeforeParameter	true
SpaceBeforeLowercaseInvocation	true
SpaceBeforeUppercaseInvocation	false
SpaceBeforeClassConstructor	false
SpaceBeforeMember	false
SpaceBeforeColon	false
SpaceAfterComma	true
SpaceBeforeSemicolon	false
SpaceAfterSemicolon	true
IndentOnTryWith	false
SpaceAroundDelimiter	true
MaxIfThenElseShortWidth	40
MaxInfixOperatorExpression	50
MaxRecordWidth	40
MaxArrayOrListWidth	40
MaxValueBindingWidth	40
MaxFunctionBindingWidth	40
MultilineBlockBracketsOnSameColumn	false
NewlineBetweenTypeDefinitionAndMembers	false
KeepIfThenInSameLine	false
MaxElmishWidth	40
SingleArgumentWebMode	false
AlignFunctionSignatureToIndentation	false
AlternativeLongMemberDefinitions	false
StrictMode	false