fix(richtext-lexical): restore selection (#10129)

Fix #9964

Now we make sure that the node for the previous selection exists before
restoring it to avoid a runtime error.

I also optimized the performance of a function in the client feature.

In the future, we should centralize the insertion of all decorator
blocks in one place. There are several things to improve. For example,
currently an additional paragraph is inserted (in addition to the one
for the selection we delete).