Separate UnicodeCache out into an own file.

Separate UnicodeCache out into an own file.

This make inclusion of unicode-inl.h in object.h absolete. Now most
compilation units don't require that header. It also breaks a cycle
within declarations of the scanner.h header.

This tries to remove includes of "-inl.h" headers from normal ".h"
headers, thereby reducing the chance of any cyclic dependencies and
decreasing the average size of our compilation units.

Note that this change still leaves 3 violations of that rule in the
code, checked with the "tools/check-inline-includes.sh" tool.

R=yangguo@chromium.org

Review URL: https://codereview.chromium.org/1287893006

Cr-Commit-Position: refs/heads/master@{#30268}