Fixes #2813: [A11y] Added label for ExplorationPlayerActivity

[rt4914]

Explanation

Fixes #2813: [A11y] Added label for ExplorationPlayerActivity

This PR does two tasks:

1. Add label so that when the ExplorationActivity opens the screen reader outputs Exploration Player instead of Oppia
2. While using screen reader it was not possible to swipe/select the toolbar title text so I have updated the click listener so that it was correctly.

You can notice both changes in before and after video.

Before PR

a11y_exploration_toolbar.mp4

After PR

correct_a11y_exploration.mp4

Checklist

• The PR title starts with "Fix #bugnum: ", followed by a short, clear summary of the changes. (If this PR fixes part of an issue, prefix the title with "Fix part of #bugnum: ...".)
• The PR explanation includes the words "Fixes #bugnum: ..." (or "Fixes part of #bugnum" if the PR only partially fixes an issue).
• The PR follows the style guide.
• The PR does not contain any unnecessary auto-generated code from Android Studio.
• The PR is made from a branch that's not called "develop".
• The PR is made from a branch that is up-to-date with "develop".
• The PR's branch is based on "develop" and not on any other branch.
• The PR is assigned to an appropriate reviewer in both the Assignees and the Reviewers sections.

[anandwana001]

LGTM

[oppiabot]

Unassigning @anandwana001 since they have already approved the PR.