* fix: support xpath= selector prefix in element resolution
Resolves#907. When a selector starts with "xpath=", use
document.evaluate() instead of document.querySelector() so that
XPath expressions like "xpath=//button" work correctly.
* test: replace overlapping test with edge case tests
Replace test_build_selector_js_xpath_strips_prefix (which overlapped
with the xpath test) with two edge case tests: empty xpath and
selector starting with "xpath" without "=" delimiter.
* fix: support xpath= selector in resolve_element_object_id
Apply the same xpath= handling to resolve_element_object_id, which is
used by type, fill, focus, hover, check, select, screenshot, drag,
and all other selector-based commands beyond basic click.
* refactor: extract build_find_element_js to deduplicate xpath/css logic
The xpath= vs querySelector branching was duplicated in both
build_selector_js and resolve_element_object_id. Extract the shared
logic into build_find_element_js and reuse it in both places.
* fix: support xpath= selector in get_element_count
Use ORDERED_NODE_SNAPSHOT_TYPE with snapshotLength for XPath counting,
matching the querySelectorAll().length behavior for CSS selectors.
* refactor: rename find to find_expr for clarity
* refactor: extract build_count_elements_js and add regression tests
Extract element counting JS generation into build_count_elements_js
helper (matching the pattern of build_find_element_js) and add tests
for both CSS and XPath counting paths.
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Co-authored-by: hyunjinee <leehj0110@kakao.com>
