Better Unicode / emoji capability detection

[itsayellow]

• I have added an entry to docs/changelog.md

Summary of changes

Closes #73.

Previously we only disallowed emojis (Unicode characters) when we detected Windows, and allowed for all other platforms. This ignored the fact that some shells in Windows are now perfectly happy displaying emojis/Unicode, while some non-Windows platforms' shells are not using a Unicode encoding and actually crash when we try to print emoji (See #73.)

This PR actually directly tests encoding our emoji unicode characters using sys.stderr.encoding to determine if it will work on a platform.

Test plan

Uninstalling a nonexistent package will show the "sleep" emoji. This should omit the emoji and not yield an error if non-Unicode encoding is used in the shell. It should show an emoji if the shell has Unicode-capable encoding.

This PR:

(venv39) > pipx uninstall doesntexist           
Nothing to uninstall for doesntexist 😴
(venv39) > LANG=en_US pipx uninstall doesntexist
Nothing to uninstall for doesntexist 

pipx 0.16.0.0:

> pipx uninstall doesntexist
Nothing to uninstall for doesntexist 😴
> LANG=en_US pipx uninstall doesntexist
Traceback (most recent call last):
  File "/home/mclapp/.local/bin/pipx", line 8, in <module>
    sys.exit(cli())
  File "/home/mclapp/.local/lib/python3.9/site-packages/pipx/main.py", line 752, in cli
    return run_pipx_command(parsed_pipx_args)
  File "/home/mclapp/.local/lib/python3.9/site-packages/pipx/main.py", line 234, in run_pipx_command
    return commands.uninstall(venv_dir, constants.LOCAL_BIN_DIR, verbose)
  File "/home/mclapp/.local/lib/python3.9/site-packages/pipx/commands/uninstall.py", line 27, in uninstall
    print(f"Nothing to uninstall for {venv_dir.name} {sleep}")
UnicodeEncodeError: 'latin-1' codec can't encode character '\U0001f634' in position 37: ordinal not in range(256)

[itsayellow]

I moved the EMOJI_SUPPORT constant and detection into emojies.py because it seemed appropriate there, but if people like it to remain in constants.py I would be amenable to that.

[uranusjr]

Is the plural of emoji emojis or emojies? The spelling is inconsistent between the commit message and the module name.

[itsayellow]

Is the plural of emoji emojis or emojies? The spelling is inconsistent between the commit message and the module name.

Yeahhhhhh. I was trying to ignore that 😛

https://www.theatlantic.com/technology/archive/2016/01/whats-the-plural-of-emoji-emojis/422763/

There is a correct answer, but no one has agreed on it yet.

It does seem that the plural is a choice between "emojis" and "emoji". So I'm going to rename the module "emojis" without the "e", since "emojies" seems unloved by everybody.

Another:
https://www.grammarly.com/blog/emojis-emoji/