feat(fmt/case): Add casing helpers

[Gustrb]

This PR implements a few casing helpers, as were asked in the issue #3125 It adds a few helpers methods such as:

• toPascalCase
• toCamelCase
• toSnakeCase
• toScreamingSnakeCase
• toKebabCase
• toTitleCase

Any suggestions on more methods would be appreciated, I've just implemented the ones I could find any use for

[CLAassistant]

All committers have signed the CLA.

[aapoalas]

Title case maybe?

[timreichen]

I think it would make more sense to have an implementation that doesn't just split by whitespaces but also other separators and by words so a case can be applied to another like in lodash. Example:

toKebabCase('Foo Bar') // => 'foo-bar'
toKebabCase('fooBar') // => 'foo-bar'
toKebabCase('__FOO_BAR__') // => 'foo-bar'

[Gustrb]

@timreichen true, it would make a lot more sense, I'll take a look at their implementation then :)

[guy-borderless]

toSentenceCase

[iuioiua]

Closing this in favour of #4082, which continues the work started here. Thank you for your contribution, @Gustrb!