Make inline blocks in GDScript more (or less) pythonic

[bojidar-bg]

Fixes #8001

From #8001 (comment) on it: (Quoting just in case)

So, testing with python3, the following are allowed:

if 1: print(1)
if 1:
  print(1)
for i in (0,1,2): print(1)

While the following are not:

if 1: print(1)
  print(2)
for i in (0,1,2): if 1: print(1)
for i in (0,1,2): if 1:
  print(1)

Currently, in GDScript, all of the first group are allowed, in addition to:

if 1: print(1)
  print(2)
for i in [0,1,2]: if 1: print(1)

With this PR, GDScript now supports the following:

for i in (0,1,2): if 1:
  print(1)
for i in (0,1,2): if 1: print(1)

But, it also drop the support for the following:

if 1: print(1)
  print(2)