Fix if types

[edemaine]

Fixes #1181:

• Allow arbitrary spaces around colon in type ternary
• Support nested interface block in if/else types

The big example from #1181 now works correctly:

export function compile<T extends CompileOptions>(src: string, options?: T): Promise<
  if T extends { ast: true }
    CivetAST
  else
    if T extends { sourceMap: true }
      code: string
      sourceMap: SourceMap
    else
      string
>
---
export function compile<T extends CompileOptions>(src: string, options?: T): Promise<
  (T extends { ast: true }?
    CivetAST
  :
    (T extends { sourceMap: true }? {
      code: string
      sourceMap: SourceMap
    }
    :
      string))
>