workaround(android placeholders): make a workaround to not have android placeholders be cut-off

[pvinis]

The type of this PR is: workaround

This PR resolves CX-1483

Description

I have added some docs in the code, but the main idea here is that ios handles long placeholders with ellipsis, and android doesn't, they are just cut-off. So instead, we now have a workaround where we can give an array of placeholders, from longest to shortest, and it will measure and use the longest string that fits in the TextInput, in our case the search field.

Here's how it looks:
https://user-images.githubusercontent.com/100233/119164903-cfb99f80-ba54-11eb-8c74-e60697573548.mov

First thing you will notice is the texts in red borders. These are the placeholders, longest to shortest. They are rendered and measured and their widths are underneath them.

Now notice on top, in the search field, the placeholder is the longest string because it fits. When the cancel button slides in, the placeholder becomes the second longest, without galleries.

In smaller devices a shorter one will be used directly, and the smallest we can show is just Search.

PR Checklist (tick all before merging)

• I have included screenshots or videos to illustrate my changes, or I have not changed anything that impacts the UI.
• I have tested my changes on iOS and Android.
• I have added tests for my changes, or my changes don't require testing, or I have included a link to a separate Jira ticket covering the tests.
• I have added a feature flag, or my changes don't require a feature flag. (How do I add one?)
• I have documented any follow-up work that this PR will require, or it does not require any.
• I have added an app state migration, or my changes do not require one. (What are migrations?)
• I have added a CHANGELOG.yml entry or my changes do not require one.

[brainbicycle]

Nice workaround! I'll give other people a chance to check it out but looks good to me.

[pvinis]

I should also note that I spoke with Jonathan and showed it to him, and he approved it, and we can remove it once the PR on rn that fixes that is merged.

[MounirDhahri]

Nice solution 🙌 this looks good to me, the only comment I had is about adding a changelog entry maybe, otherwise please feel free to merge

[pvinis]

Now that the new changelog flow is almost here, I'm kinda tired of the old conflicts. I don't want to spend another second fixing changelog conflicts anymore. I much prefer spending some time helping with the new flow if there's anything needed there.