tools: command-regexp functions shouldn't be public

[dgw]

The major rule-system rework in #1873 is a great excuse to take the get_*_regexp() and get_*_pattern() functions from sopel.tools and either shove them into someplace like sopel.plugins.rules.utils or encapsulate the pattern generation into the different rule object classes.

@Exirel let's come back to this after #1873 is finished.

Full to-deprecate list (for 7.1):

• compile_rule() [tools, loader, plugins.rules: deprecate compile_rule #2027]
• get_command_regexp() [plugins: command-regexp functions are now private #1944]
• get_command_pattern() [plugins: command-regexp functions are now private #1944]
• get_nickname_command_regexp() [plugins: command-regexp functions are now private #1944]
• get_nickname_command_pattern() [plugins: command-regexp functions are now private #1944]
• get_action_command_regexp() [plugins: command-regexp functions are now private #1944]
• get_action_command_pattern() [plugins: command-regexp functions are now private #1944]

Full to-delete list (for 8.0):

• compile_rule() [tools: follow through on all removed_in='8.0' deprecations #2141]
• get_command_regexp() [tools: follow through on all removed_in='8.0' deprecations #2141]
• get_command_pattern() [tools: follow through on all removed_in='8.0' deprecations #2141]
• get_nickname_command_regexp() [tools: follow through on all removed_in='8.0' deprecations #2141]
• get_nickname_command_pattern() [tools: follow through on all removed_in='8.0' deprecations #2141]
• get_action_command_regexp() [tools: follow through on all removed_in='8.0' deprecations #2141]
• get_action_command_pattern() [tools: follow through on all removed_in='8.0' deprecations #2141]

[dgw]

Updating the OP based on discussion in #1944 (comment)

[dgw]

This wasn't supposed to be auto-closed. Whoops.

[dgw]

The rest of this is for 8.0; reassigning milestone.