Add "helloworld" & "runtime" tests for newer .NET and Ballerina runtimes

[mrutkows]

Currently, we have "helloworld" tests for other langs and need some equivalency for newer runtime langs. of .NET and Ballerina. Here is what we have now for "helloworld":

./tests/src/integration/export/manifest_helloworld.yaml:          runtime: nodejs:6
./tests/src/integration/export/manifest_helloworld.yaml:          runtime: java
./tests/src/integration/export/manifest_helloworld.yaml:          runtime: python
./tests/src/integration/export/manifest_helloworld.yaml:          runtime: swift:3.1.1
./tests/src/integration/helloworld/manifest.yaml:                      runtime: ruby:2.5

or some "helloXXX" variant:

./tests/src/integration/helloworld/manifest.yaml:                      runtime: go:1.11
./tests/dat/manifest_hello_swift.yaml:                                        runtime: swift

and "runtime" (version) variants for:

./tests/src/integration/runtimetests/manifest.yaml:                runtime: nodejs:8
./tests/src/integration/runtimetests/manifest.yaml:                runtime: php:7.1
./tests/src/integration/runtimetests/manifest.yaml:                runtime: php:7.2
./tests/src/integration/runtimetests/manifest.yaml:                runtime: php:7.3
./tests/src/integration/runtimetests/manifest.yaml:                runtime: php
./tests/src/integration/runtimetests/manifest.yaml:                runtime: python
./tests/src/integration/runtimetests/manifest.yaml:                runtime: python:2
./tests/src/integration/runtimetests/manifest.yaml:                runtime: python:3
./tests/src/integration/runtimetests/manifest.yaml:                runtime: ruby:2.5
./tests/src/integration/runtimetests/manifest.yaml:                runtime: swift:4.2

NOTE: we SHOULD have helloworld tests use "default" kind (not versioned) for each runtime language and a runtime test for each supported version. A PR to fix this issue SHOULD attempt to comprehensively fix the uniformity of tests accordingly.

[ and not have "default" kinds be tested as a side effect on another testcase of different purpose.]

[kingledion]

Helloworld test for Rust is added with this MR: #1119