The lexer now splits interpolation tokens out from attribute value tokens.
Previously the attribute value of `<div attr="Hello, {{ name}}">` would be a single
token. Now it will be three tokens:
```
ATTR_VALUE_TEXT: "Hello, "
ATTR_VALUE_INTERPOLATION: "{{", " name", "}}"
ATTR_VALUE_TEXT: ""
```
- ATTR_VALUE_INTERPOLATION tokens have three parts, "start marker",
"expression" and "end marker".
- ATTR_VALUE_INTERPOLATION tokens are always preceded and followed
by TEXT tokens, even if they represent an empty string.
The HTML parser has been modified to recombine these tokens to allow this
refactoring to have limited effect in this commit. Further refactorings
to use these new tokens will follow in subsequent commits.
PR Close#42062
c516e252fc