fundamental: move several macros and functions into src/fundamental/

sd-boot has a copy of a subset of codes from libbasic. This makes
sd-boot share the code with libbasic, and dedup the code.

Note, startswith_no_case() is dropped from sd-boot, as
- it is not used,
- the previous implementation is not correct,
- gnu-efi does not have StrniCmp() or so.

src/shared/efi-loader-features.h

@@ -1 +0,0 @@
-../boot/efi/loader-features.h

src/shared/meson.build

@@ -89,7 +89,6 @@ shared_sources = files('''
         dns-domain.h
         dropin.c
         dropin.h
-        efi-loader-features.h
         efi-loader.c
         efi-loader.h
         enable-mempool.c