feat: 5 new commands to toggle text between PascalCase, camelCase, snake_case, Title Case and kebab-case

[nikitarevenco]

This PR introduces a new mode under ` called "case" mode which has several utility keymappings for working with switching case of text

switch_to_lowercase and switch_to_uppercase have been moved to this new mode. 5 new commands have been added and are accessible under ` aswell:

Key	Description	Command
l	Switch all text to lowercase	switch_to_lowercase
u	Switch all text to UPPERCASE	switch_to_uppercase
p	Switch text to Pascal Case	switch_to_pascal_case
c	Switch text to camelCase	switch_to_camel_case
t	Switch text to Title Case	switch_to_title_case
s	Switch text to snake_case	switch_to_snake_case
k	Switch text to kebab-case	switch_to_kebab_case