Upgrade to Python 3.9 syntax

[bkeryan]

• This contribution adheres to CONTRIBUTING.md.

• I've updated CHANGELOG.md if applicable.

• I've added tests applicable for this pull request

What does this Pull Request accomplish?

Use PEP 585 – Type Hinting Generics In Standard Collections and do other Python 3.9 syntax upgrades:

• Ran Get-ChildItem -Recurse "*.py" | ForEach-Object { pyupgrade --py39-plus $_ } using the latest pyupgrade (installed via pipx).

Use PEP 604 – Allow writing union types as X | Y where possible:

• Added from __future__ import annotations to most files containing from typing import .... This allows using type hint syntax from the future.
• Re-ran pyupgrade. This uses X | Y syntax if the file already has from __future__ import annotations.

I did not remove the hardcoded Optional[...] references from docstrings.

Why should this Pull Request be merged?

Reduce number of typing imports.

Remove usage of typing.Optional, which people often confuse with default arguments.

What testing has been done?

Ran ni-python-styleguide, mypy, and pytest locally.

[github-actions]

Test Results

    34 files  ±0      34 suites  ±0   54m 10s ⏱️ - 1m 46s
 2 382 tests ±0   2 026 ✅  -  2    356 💤 + 2  0 ❌ ±0 
42 864 runs  ±0  36 602 ✅  - 10  6 262 💤 +10  0 ❌ ±0 

Results for commit 143fb05. ± Comparison against base commit fcddb56.

This pull request skips 2 tests.

tests.component.test_interpreter ‑ test___error_code_with_hardcoded_error_message___get_error_string___returns_hardcoded_error_message[grpc_init_kwargs--200284]
tests.component.test_interpreter ‑ test___error_code_with_hardcoded_error_message___get_error_string___returns_hardcoded_error_message[grpc_init_kwargs-DAQmxErrors.SAMPLES_NOT_YET_AVAILABLE]