fix: cursor placement clicking inside Entry widget

[chrisbirster]

Description:

Reproducible in the fyne_demo app where clicking the empty space inside the multi-line entry widget causes the cursor to jump to the beginning of row instead of the end.

Before:
https://user-images.githubusercontent.com/15853349/165876725-6d6e9eda-6f07-4208-9d48-300dcefda69d.mov

After:
https://user-images.githubusercontent.com/15853349/165876757-0e5fed20-e22b-4acd-8ba1-a40602eb2c69.mov

Fixes #2877

Checklist:

• Tests included.
• Lint and formatter run with no errors.
• Tests all pass.

[coveralls]

Coverage remained the same at 61.638% when pulling f763182 on chrisbirster:entry-empy-space into c36764a on fyne-io:develop.

[andydotxyz]

Great, thanks!