Completions: Add multi-line heuristics for C, C++, C#, and Java

[philipp-spiess]

The title says it all. They're all c-like so the implementation doesn't need to change.

I also noticed that we currently do not support this style of syntax for else-block continuation. I don't think it's a big issue though since the single line } would end the selection so it's not as noticible as in the single line case. E.g. compare this cut-off behavior:

This:

if ()
{
  // foo
} 

With this:

if ()
{
  // foo
} else {

And it's clear as to why this is only an issue in the single line case

Test plan

• Big test coverage this time

[sourcegraph-bot]

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