Fix resolve and completion for subcomponents and methods

[hurricup]

Looks like atm we are working only with subcomponents in the current file, wihout any inheritance. And do not work with methods at all.

Also feels like we should lex slugs separately: SELF:, PARENT: and REQUEST:

• https://metacpan.org/dist/HTML-Mason/view/lib/HTML/Mason/Devel.pod#%3C%def-name%3E
• https://metacpan.org/dist/HTML-Mason/view/lib/HTML/Mason/Devel.pod#Accessing-methods-and-attributes