[Development] proposed clang-format improvements for lambda functions

[Tim Blechmann]

i'd like to propose the following improvements to the clang-format:

AllowShortLambdasOnASingleLine: None
LambdaBodyIndentation: OuterScope

rationale:
* single-line lambda functions are harmful, as one cannot set different 
breakpoints for construction and invocation of the lambda function.
* indent lambda bodies at the outer scope, so that the indentation 
reflects the nesting level.


currently we get:

> void foo(auto);
> 
> void bar()
> {
>     return foo([] { foo([] { return 0; }); });
> }
> 
> void foooo(int, auto);
> 
> void baz()
> {
>     return foooo(0, [] {
>         foo([] {
>             auto x = 1 + 1;
>             return x;
>         });
>     });
> 
>     return foooo(
>             iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiint,
>             [] {
>                 foo([] {
>                     auto x = 1 + 1;
>                     return x;
>                 });
>             });
> }

after the proposed changes, we'd end up with:

> void foo(auto);
> 
> void bar()
> {
>     return foo([] {
>         foo([] {
>             return 0;
>         });
>     });
> }
> 
> void foooo(int, auto);
> 
> void baz()
> {
>     return foooo(0, [] {
>         foo([] {
>             auto x = 1 + 1;
>             return x;
>         });
>     });
> 
>     return foooo(
>             iiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiiint,
>             [] {
>         foo([] {
>             auto x = 1 + 1;
>             return x;
>         });
>     });
> }

opinions?