test: extract common status helper functions

Create `pkg/reconciler/testing/status.go` and move status related
helper functions for `TaskRun/CustomRun` and later `PipelineRun` there.
Remove duplication from helper functions.

Move yaml parsing helper functions to `test/parse/yaml.go`.

Rename import `ttesting ==> th`, short for "testing helpers".

Issue #8760, #7166.

Signed-off-by: Stanislav Jakuschevskij <[email protected]>

Author: twoGiants