Fix the types for isComment and isText

[skirtles-code]

The types for isComment and isText were using Comment and Text incorrectly.

Both Comment and Text were being imported from vue, but they weren't actually being used for the types of those two functions. Those values are both symbols, not types, so they were ignored in the type annotation. Instead, the global Comment and Text types, used for DOM nodes, were being used.

The simplest fix was to use typeof Comment and typeof Text, but to avoid future clashes I've renamed all the imported symbols to have less problematic names.

The docs have been updated accordingly, though they still use the original names for the symbols.