Unicode/EBCDIC decode fixes and validator functions

[Rot127]

Your checklist for this pull request

• I've read the guidelines for contributing to this repository.
• I made sure to follow the project's coding style.
• I've documented every RZ_API function and struct this PR changes.
• I've added tests that prove my changes are effective (required for changes to RZ_API).
• I've updated the Rizin book with the relevant information (if needed).

Detailed description

• Fix UTF32 decode. The number of consumed bytes were incorrect. UTF-32 is fixed length.
• Adds Unicode validator functions for UTF-32 and EBCDIC.

Test plan

Added

Closing issues

closes #4697

[wargio]

Suggested change

	RZ_API bool rz_utf32_valid_cp(const ut8 *buf, size_t buf_len, bool big_endian);
	RZ_API bool rz_utf32_valid_codepoint(const ut8 *buf, size_t buf_len, bool big_endian);

Avoid using cp in function names.

[notxvilka]

These breaks are worrying:

[XX] 268 ms   db/formats/elf/strings iz (utf-32le)
RZ_NOPLUGINS=1 /usr/bin/rizin -escr.utf8=0 -escr.color=0 -escr.interactive=0 -eflirt.sigdb.load.system=false -eflirt.sigdb.load.home=false -N -qc 'iz~Hello
fl@F:strings
s sym.main
af
pdf~str.Hello
aar
fl@F:strings
' bins/elf/analysis/hello-utf-32le
-- stdout
--- expected
+++ actual
@@ -1,6 +1,6 @@
   0 0x000005e8 0x004005e8  12   52 .rodata utf32le Hello World\n
 0x004005e8 52 str.Hello_World
 0x00400620 32 str.S
-|           0x0040052e      mov   qword [var_10h], str.Hello_World     ; 0x4005e8 ; U"Hello World\n"
+|           0x0040052e      mov   qword [var_10h], str.Hello_World     ; 0x4005e8 ; U"\U00000048\U00000065\U0000006c\U0000006c\U0000006f\U00000020\U00000057\U0000006f\U00000072\U0000006c\U00000064\U0000000a"
 0x004005e8 52 str.Hello_World
 0x00400620 32 str.S