[V3 Utils] Make markdown helpers escape special chars

[Tobotimus]

Feature request

Select the type of feature you are requesting:

• API functionality

Describe your requested feature

Currently we have a bunch of helpers in redbot.core.utils.chat_formatting, including those which simply return some string formatted in some way with markdown, i.e. bold, italics, inline etc. All they do now is wrap the input string in the formatting delimiters and return - people are more likely to do this by just including the delims in their raw string, since it takes up less characters and doesn't require an import.

A way to actually make these functions useful would be to have them escape any relevant markdown formatting syntax within the input string.

Examples

Inline

Current behaviour:

>>> inline("a string` containing` backticks")
"`a string` containing` backticks`"

Formatted: a string containing backticks

After changes:

>>> inline("a string` containing` backticks")
"``a string` containing` backticks``"

Formatted: a string` containing` backticks

Italics

Current behaviour:

>>> italics("A string* containing *asterisks")
"*A string* containing *asterisks*"

Formatted: A string containing asterisks

After changes:

>>> italics("A string* containing *asterisks")
"*A string\* containing \*asterisks*"

Formatted: A string* containing *asterisks

[Tobotimus]

Partially resolved by #2182, the unresolved ones don't seem to be solve-able right now.