M*LIB: non-inlined strings, FuriString primitive (#1795)
* Quicksave 1
* Header stage complete
* Source stage complete
* Lint & merge fixes
* Includes
* Documentation step 1
* FBT: output free size considering BT STACK
* Documentation step 2
* py lint
* Fix music player plugin
* unit test stage 1: string allocator, mem, getters, setters, appends, compare, search.
* unit test: string equality
* unit test: string replace
* unit test: string start_with, end_with
* unit test: string trim
* unit test: utf-8
* Rename
* Revert fw_size changes
* Simplify CLI backspace handling
* Simplify CLI character insert
* Merge fixes
* Furi: correct filenaming and spelling
* Bt: remove furi string include
Co-authored-by: Aleksandr Kutuzov <alleteam@gmail.com>
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