ProgmemStringRef owns write_to() and equals() with the platform split, so the
EntityBase accessors are inline forwarders. Adds ESPHOME_ENTITY_NAME_MAX_LEN
mirroring NAME_MAX_LENGTH and tidies the codegen and tests.
Inline get_name_to() off ESP8266, add write_name_to() and name_equals() so
web_server avoids copies, always emit ESPHOME_PSTR, and follow the get_icon()
pattern: get_name() is a static_assert stub on ESP8266 and ESPDEPRECATED
elsewhere until 2027.5.0.
J. Nick Koston