ts: add compile_artifact, ignore_extension flag

In b5213542 the testsuite gained the
capability to collect generic metrics. But this assumed that the test
was not linking and producing artifacts and we only wanted to track
object files, interface files, or build artifacts from the compiler
build. However, some backends, such as the JS backend, produce artifacts when
compiling, such as the jsexe directory which we want to track.

This patch:

- tweaks the testsuite to collect generic metrics on any build artifact
in the test directory.

- expands the exe_extension function to consider windows and adds the
ignore_extension flag.

- Modifies certain tests to add the ignore_extension flag. Tests such as
heaprof002 expect a .ps file, but on windows without ignore_extensions
the testsuite will look for foo.exe.ps. Hence the flag.

- adds the size_hello_artifact test