Allow "emoji presentation selector" in emoji-only sequences when parsing for big emoji display

[smithfred]

Some native OS emoji pickers (e.g. GNOME) explicitly add, after the inserted emoji, the "emoji presentation character" U+FE0F, which is an explicit request to present the previous character as an emoji instead of a text character - see https://www.unicode.org/reports/tr51/#Emoji_Variation_Sequences

The big emoji logic doesn't handle this character being present, so emoji sequences inserted this way end up small.

To reproduce

For each of the below emoji sequences, copy/paste into the message field and hit Enter. The first sequence has a U+FE0F between the first emoji and the space. The second doesn't.

1. 😄️ 😄

2. 😄 😄

Actual result

1. Small emoji.
2. Big emoji.

Expected result

1. Big emoji.
2. Big emoji.

[smithfred]

Additional info: https://www.unicode.org/reports/tr51/tr51-15.html#Presentation_Style

Although arguably an emoji picker adding the emoji presentation selector to a character with only an emoji presentation is pointless and likely to lead to bugs like the above, it makes sense to do so when the character has two possible presentations, so Element should handle this correctly.

I will file a bug with GNOME (actually GTK) separately about only using it when necessary.