template and generic prepass is un-necessary and causes bugs

[timotheecour]

generic prepass is bad

links:

• D20201026T051952
• [Meta] Generics/Static early symbol resolution · Issue #8677 · nim-lang/Nim
• generic sandwich problem #236

also might be root cause for issues like:

• template lookup fails with nested generic types nim-lang/Nim#9494

• Cannot explicitly instantiate a generic template inside a generic proc nim-lang/Nim#12905

• Symbol binding bug with generics and template nim-lang/Nim#12683

• https://nim-lang.org/docs/manual.html#templates-limitations-of-the-method-call-syntax

• breaks optional parameters (eg cmp[T]) even when those aren't used for a given T, see add algorithm.merge nim-lang/Nim#16182 (comment)

likewise for template pre-pass

causes:

• https://nim-lang.github.io/Nim/manual.html#templates-limitations-of-the-method-call-syntax
• Error on method call syntax within a template nim-lang/Nim#7085
• Illegal symbol reuse in template with method call syntax nim-lang/Nim#14844 + many others

here's another example:

when true: # D20201207T194715
  template fn=
    type Dollar = distinct int
    let a1 = 1
    let a2 = a1.Dollar
  fn()

=> Error: undeclared field: 'Dollar'

TODO

see what should be a proper fix for nim-lang#11167 without generic prepass