uuid: support uuid comparison with strings

Before this patch it was impossible to compare uuid values with
string representations of uuid. However we have cases when such
comparisons is possible (e.g. "decimal" where we can compare
decimal values with strings and numbers).

This patch extends uuid comparators (__eq, __lt and __le) and
every string argument is tried to be converted to uuid value to
compare then.

Follow-up #5511

@TarantoolBot document
Title: uuid comparison rules

Currently comparison between uuid values is supported.

Example:
```lua
u1 = uuid.fromstr('aaaaaaaa-aaaa-4000-b000-000000000001')
u2 = uuid.fromstr('bbbbbbbb-bbbb-4000-b000-000000000001')

u1 > u2  -- false
u1 >= u2 -- false
u1 <= u2 -- true
u1 < u2  -- true
```

Also it's possible to compare uuid values with its string
representations:
```lua
u1_str = 'aaaaaaaa-aaaa-4000-b000-000000000001'
u1 = uuid.fromstr(u1_str)
u2_str = 'bbbbbbbb-bbbb-4000-b000-000000000001'

u1 == u1_str -- true
u1 == u2_str -- false

u1 >= u1_str -- true
u1 < u2_str  -- true
```