stop escaping via initialization of 'this'

[WalterBright]

No description provided.

[MartinNowak]

Rebased onto scope after merging #6332. Apparently this broke one of the tests (or that was broken), see https://github.com/dlang/dmd/pull/6331/files#diff-33b3e2fefc5298c0b9de67897929e7ceR367.
Also changed to use #line pragmas to make the tests position independent.

[MartinNowak]

Broke phobos again, std.array.replaceLast can't be safe because it ends up calling std.algorithm.searching.simpleMindedFind.
If you mark all of them @safe dmd complains about escaping the needle parameter through a range.save call.

std/algorithm/searching.d(2016): Error: scope variable needle assigned to non-scope parameter this calling std.range.retro!string.retro.Result!().Result.save

Apparently the check at https://github.com/dlang/dmd/pull/6331/files#diff-b86664e5c05fae51686b37d9e58043c9R9977 is not guarded by params.vsafe.

[MartinNowak]

See #6340