A text layer's name followed its Source Text whenever the name started with "Text", so a user's
"Text Title" was replaced by the next text edit. The layer now records whether its name follows
the text (`name_follows_text`, optional in the project file). A new text layer named after its
text follows it; a name given at creation or by Rename (Enter, layer.rename, a script's
layer.name, Layer Settings' name) is the user's and stays; renaming to an empty name shows the
text again and follows it; committing the unchanged name changes nothing; copies keep the state.
On-canvas typing and layer.setText share the rule. The name is the text's first paragraph, which
ends at a line feed or a bare carriage return (After Effects' paragraph break).
Projects saved without the state keep the old rule for the names that followed: a name that is
empty, the text's own, or "Text"/"Text 2"... follows; any other name stays. AEP import records a
stored layer name as the user's and no name as following, and names an empty text layer without
a name "Text" instead of "Layer"; export writes no name for a following layer and keeps the name
the user gave, even when it equals the text.
Fixes#3233
vangel76